Router bit bearings: size charts, top vs bottom guides and replacement
A router-bit guide bearing follows an edge or template while the cutter removes material. Choose a replacement by the bit manufacturer’s part reference and the bearing’s outside diameter, bore, width and retention arrangement. A “1/4 inch router bit” usually identifies its shank or cutter, not necessarily the bearing bore.
On this page17 sections ⌄
Top bearing vs bottom bearing vs double bearing
A router table turns the tool upside down, but shank-side and tip-side remain unambiguous. Select the guide location from where the template actually sits. “Pattern”, “template” and “flush trim” are not complete dimensional specifications.
On smaller screens, scroll the table sideways to read all columns.
| Layout | What it means | What to verify |
|---|---|---|
| Top / shank-side bearing | Guide beside the shank, behind the cutting length | The template must meet that guide along the intended cut |
| Bottom / tip-side bearing | Guide beyond the cutter, at the tip end | The template or finished edge must be reachable by that guide |
| Top-and-bottom arrangement | Guides on both sides of the cutting section | Confirm both locations in the exact drawing; do not assume every double-bearing bit has this arrangement |
| Two adjacent bearings | A pair of guides mounted together | CMT’s double-bearing spiral family is a separate layout to identify by drawing, not a promise of top-and-bottom guidance |
| Guide bushing | A stationary guide attached to the router base | Different offset and clearance rules from a rotating bit-mounted bearing |
Which size does 1/4, 1/2 or 1/8 inch describe?
Use a clean, undamaged reference part or the manufacturer’s drawing. Record which dimension an inch value refers to before converting it. One inch is exactly 25.4 mm; catalogue nominal labels may be rounded, so do not replace a stated 19 mm part with an assumed 19.05 mm part merely because both are called 3/4 inch.
On smaller screens, scroll the table sideways to read all columns.
| Dimension | Function | Example of a misleading shortcut |
|---|---|---|
| Shank diameter | Fits the router collet | A 1/4 in shank does not prove a 1/4 in bearing bore |
| Bearing bore / ID | Fits the specific bearing seat or journal | A tip-mounted bearing can run on a smaller journal than the shank |
| Bearing OD | Follows the template and controls lateral offset | A 1/2 in OD bearing is not a 1/2 in bore bearing |
| Bearing width | Fits between shoulders, shields and retention hardware | Same ID and OD with a different width can prevent correct retention |
| Cutter diameter and cutting length | Determine the material-removal envelope | Neither is the bearing width |
CMT 791 guide-bearing size chart
Selected conventional bearing rows from the 2026 CMT catalogue, printed page 436. All three dimensions below are the listed millimetre values: D = outside diameter, B = bore, P = width. The table does not assert cross-brand interchangeability.
On smaller screens, scroll the table sideways to read all columns.
| CMT part | OD D mm | Bore B mm | Width P mm |
|---|---|---|---|
| 791.035.00 | 6.35 | 3.17 | 2.8 |
| 791.062.00 | 9.3 | 4.76 | 3.17 |
| 791.002.00 | 9.5 | 4.76 | 3.2 |
| 791.063.00 | 12.5 | 4.76 | 4.98 |
| 791.003.00 | 12.7 | 4.76 | 5 |
| 791.010.00 | 12.7 | 6.35 | 4.8 |
| 791.022.00 | 13 | 5 | 4 |
| 791.023.00 | 13 | 6 | 5 |
| 791.024.00 | 15 | 6 | 5 |
| 791.018.00 | 15.88 | 4.76 | 5 |
| 791.009.00 | 15.88 | 6.35 | 5 |
| 791.006.00 | 16 | 5 | 5 |
| 791.025.00 | 16 | 8 | 5 |
| 791.019.00 | 19 | 4.76 | 7.5 |
| 791.007.00 | 19 | 6 | 6 |
| 791.004.00 | 19.05 | 6.35 | 7 |
| 791.034.00 | 19 | 8 | 6 |
| 791.011.00 | 19 | 12.7 | 4 |
| 791.012.00 | 22 | 8 | 6 |
| 791.005.00 | 22 | 8 | 7 |
| 791.017.00 | 22.2 | 4.76 | 7.5 |
| 791.021.00 | 22.2 | 9.53 | 7 |
| 791.013.00 | 22.2 | 12.7 | 7 |
| 791.036.00 | 24 | 8 | 8 |
| 791.037.00 | 28 | 8 | 9 |
| 791.026.00 | 28 | 12 | 8 |
| 791.014.00 | 28.5 | 4.76 | 8.4 |
| 791.030.00 | 28.5 | 8 | 8.5 |
| 791.027.00 | 28.5 | 12.7 | 8 |
| 791.033.00 | 31.7 | 8 | 5 |
| 791.015.00 | 31.7 | 12.7 | 8 |
| 791.016.00 | 34.9 | 4.76 | 11.5 |
| 791.031.00 | 34.9 | 8 | 11.6 |
| 791.029.00 | 34.9 | 12.7 | 11 |
| 791.028.00 | 37 | 12 | 12 |
| 791.020.00 | 38.1 | 12.7 | 13.3 |
Undersize guides after resharpening: do not round them away
CMT identifies 791.062.00, OD 9.3 mm, as the resharpening alternative to 791.002.00, OD 9.5 mm; 791.063.00, OD 12.5 mm, is the alternative to 791.003.00, OD 12.7 mm. The 2026 table is used here because the web table groups some dimensions differently.
An undersize guide intentionally changes the relationship between the guide and the resharpened cutter. It is not the default replacement for a new bit. Have the actual cutter and finished profile checked; do not choose a smaller bearing simply to make a damaged cutter reach further.
Freud replacement bearing dimensions and listed speed limits
Exact 62-series product records available in Freud’s 62-108 product page. Units remain as published. “Height” is Freud’s minor-height field; confirm the assembly drawing and the correct part for the bit.
On smaller screens, scroll the table sideways to read all columns.
| Freud part | Type | Outside diameter | Bore | Height | Listed max rpm |
|---|---|---|---|---|---|
| 62-100 | Steel | 3/8 in | 1/8 in | 5/32 in | 24000 |
| 62-102 | Steel | 3/8 in | 3/16 in | 1/8 in | 24000 |
| 62-103 | Steel | 1/2 in | 1/4 in | 3/16 in | 24000 |
| 62-104 | Steel | 1/2 in | 3/16 in | 3/16 in | 24000 |
| 62-105 | Steel | 19 mm | 10 mm | 7 mm | 24000 |
| 62-106 | Steel | 3/4 in | 1/4 in | 9/32 in | 24000 |
| 62-107 | Steel | 7/8 in | 5/16 in | 9/32 in | 24000 |
| 62-108 | Steel | 22 mm | 8 mm | 7 mm | 24000 |
| 62-110 | Sleeved | 3/4 in | 3/16 in | 5/16 in | 24000 |
| 62-112 | Steel | 5/8 in | 1/4 in | 3/16 in | 24000 |
| 62-114 | Steel | 1-1/8 in | 1/2 in | 5/16 in | 18000 |
| 62-116 | Steel | 1-3/8 in | 1/2 in | 7/16 in | 16000 |
| 62-120 | Sleeved | 1 in | 5/16 in | 10 mm | 24000 |
| 62-121 | Sleeved | 1-1/4 in | 5/16 in | 10 mm | 18000 |
| 62-122 | Sleeved | 1-1/2 in | 5/16 in | 10 mm | 16000 |
| 62-124 | Sleeved | 26 mm | 5/16 in | 7 mm | 24000 |
| 62-128 | Sleeved | 30 mm | 5/16 in | 7 mm | 24000 |
| 62-136 | Sleeved | 2 in | 17 mm | 10 mm | 16000 |
| 62-139 | Sleeved | 1-1/2 in | 15 mm | 5/16 in | 16000 |
Does a 24,000 rpm bearing allow any bit to run at 24,000 rpm?
No. The complete cutter, arbor, bearing, router and setup must all remain within their applicable limits. The 32-504 rabbeting set, for example, lists 16,000 rpm. A higher replacement-bearing number does not override that tool limit.
Whiteside 3000, 3000A and B9: shank, cut length and guide
On smaller screens, scroll the table sideways to read all columns.
| Template bit | Shank | Cutting diameter | Cutting length | Overall length | Listed bearing |
|---|---|---|---|---|---|
| 3000A | 1/4 in | 1/2 in | 1/8 in | 1-3/4 in | B9 |
| 3000 | 1/4 in | 1/2 in | 1/4 in | 1-7/8 in | B9 |
| 3001 | 1/4 in | 1/2 in | 1/2 in | 2 in | B9 |
| 3002 | 1/4 in | 1/2 in | 3/4 in | 2-1/4 in | B9 |
| 3004 | 1/4 in | 1/2 in | 1 in | 2-1/2 in | B9 |
| 3006 | 1/4 in | 5/8 in | 1/4 in | 1-3/4 in | B6 |
What bearing does Whiteside 3000 use?
Whiteside’s template-family table identifies B9. Its bearing table gives B9 a 1/2 in OD and 1/4 in ID. The 3000A has a shorter cutting length than 3000; they are not the same complete bit.
Is B9U identical to B9?
No. B9U is listed at 0.490 in OD for resharpening, with a 1/4 in ID. B9 is 1/2 in OD. Do not erase the U suffix or substitute by bore alone.
Rabbeting bearing sets and the depth calculation
For a straight cylindrical cutter following a straight reference edge, lateral cut depth is (cutter diameter − bearing diameter) ÷ 2. With a 1-3/8 in cutter and a 5/8 in guide, the geometric depth is (1.375 − 0.625) ÷ 2 = 0.375 in, or 3/8 in. This is radial depth, not the axial height of the rabbet.
A guide with the same effective diameter as that straight cutter gives zero offset, or flush trimming. A larger guide reduces the cut; a smaller guide increases it. Profiled cutters, conical guides and guide bushings need their own geometry, so the simple equation is not a universal profile calculator.
On smaller screens, scroll the table sideways to read all columns.
| Named set | Manufacturer-scoped reference | Important distinction |
|---|---|---|
| CMT 835.001.11 | 1/4 in shank, 1-3/8 in cutter, six interchangeable guides; kit 791.703.00 | Six-guide set does not mean any six bearings of the right bore will work |
| CMT 835.501.11 | 1/2 in shank, 1-3/8 in cutter; kit 791.703.00 | Different shank, explicitly listed kit |
| Freud 32-504 | 1/4 in shank, 1-3/8 in cutter; flush, 1/8, 1/4, 5/16, 3/8, 7/16 and 1/2 in cut depths | The exact page lists a 16,000 rpm maximum; follow its complete assembly instructions |
Spiral, compression, bowl and edge-profile bits
A bearing guides the path; it does not turn a wood-cutting tool into a metal-cutting tool. Router bearings for aluminium machining require the exact cutter material and application approval. CNC linear guides and the router motor’s internal spindle bearings are separate components.
On smaller screens, scroll the table sideways to read all columns.
| Requirement | Reference or selection rule | Boundary |
|---|---|---|
| Upcut spiral with guides | CMT 191.008.11B: 6.35 mm cutter and shank, 25.4 mm cutting length, bearing 791.035.00 | The bearing bore is 3.17 mm in the referenced bearing table, not the shank diameter |
| Downcut spiral with guides | CMT 192.008.11B: same listed 6.35 mm cutter/shank and 25.4 mm cutting length; bearing 791.035.00 | Upcut and downcut flute directions are different even when guide dimensions match |
| Compression / combined upcut and downcut | CMT 190.508.11B: 12.7 mm cutter and shank, 47.6 mm cutting length; bearing 791.010.00 | Workpiece thickness and the transition between flute directions still need the tool instructions |
| Bowl and tray profiles | CMT 7/851B identifies a dedicated bearing-guided profile range | A straight flush-trim bearing example does not specify the radius, plunge capability or complete bowl bit |
| Roundover, chamfer, cove, dovetail, slot and mortise | Match the complete profile and the maker’s spare-part drawing | The words top bearing do not establish the required angle, radius, depth or safe plunge method |
Replacement, cleaning, lubrication and failure checks
Keep shields and stepped washers in the manufacturer’s orientation; CMT specifically calls out correct orientation of its black washer. Do not omit hardware to make an incorrect bearing fit. Retention and free guide rotation are both necessary.
These are guide-bearing checks, not instructions to rebuild a Bosch, DeWalt, Porter-Cable or other router motor. Internal motor-bearing replacement needs the exact equipment service procedure, electrical isolation and specified parts. A generic guide-bearing chart cannot establish that fitment.
On smaller screens, scroll the table sideways to read all columns.
| Observation | Check with power isolated | Decision |
|---|---|---|
| Rough, seized or loose guide | Bearing feel, visible damage, seat and retention hardware | Use the specified replacement; do not compensate by pushing harder |
| Scorching or an unexpected step | Guide rotation, actual OD, cutter condition and template contact | Stop and determine the cause before another cut |
| Bearing binds after reassembly | Width, shield orientation, spacers and screw/collar arrangement | Correct the assembly; never leave retention loose just to free the bearing |
| Resin or dust around the guide | Maker’s cleaning procedure and seal compatibility | External cleaning is not permission to soak a sealed bearing |
| Lubricant question | Whether the exact guide is sealed/prelubricated and serviceable | Do not add an arbitrary oil or grease to a sealed guide; no universal lubricant grade is specified here |
Common router-bearing questions
Can I use a router bit without its bearing?
Not by simply removing a guide from a tool designed to use it. A non-bearing bit needs a supported guidance method and a tool/setup approved for that use. Freehand operation is not a substitute for the missing guide.
Does a sealed bearing have to be oiled?
Sealed and prelubricated does not imply user-serviceable. Follow the exact maker’s instructions. Oil added around the outside may attract dust without restoring a worn internal contact.
Can two brands be interchanged if their dimensions match?
Matching ID, OD and width only creates a dimensional candidate. Guide surface, shield/retention geometry, speed, tolerances and the bit maker’s approval still matter.
What information should I record before looking for a replacement?
Bit brand and number, bearing marking, guide position, ID/OD/width, shield and retention details, cutter condition, and whether it has been resharpened. That identifies the job more reliably than “1/4 inch bearing”.
What the evidence can — and cannot — tell you
| Observation or context | Interpretation to consider | Verification needed |
|---|---|---|
| Bearing size | Outside diameter, bore and width | Do not order from shank diameter alone. |
| Guide position | Shank-side, tip-side or an exact double-bearing layout | Top and bottom are relative to the bit, not gravity. |
| Cut geometry | Cutter diameter, guide diameter and template position | Changing the bearing changes the offset or profile. |
| Assembly limits | Correct shields, screw/collar, speed and tool condition | A bearing rating cannot raise the complete tool’s limit. |
Plan the work safely
Identify and record
Isolate the router from power and remove the bit by its equipment instructions. Record the bit number, original bearing number, positions of screws, shields, spacers and collars before dismantling.
Check the context
Match the manufacturer’s spare part. Measure bearing outside diameter, bore and width separately from shank and cutter diameters. Check whether the cutter has been professionally resharpened and needs a specified undersize guide.
Verify before acting
Reassemble with the specified retention hardware and orientation. Support the correct surfaces without striking cutting edges. Follow the bit maker’s tightening instructions; this reference does not invent a universal screw torque.
Keep the decision traceable
With power disconnected, check that the guide rotates freely, retention is secure and the assembly has the required clearance. Restore guards and follow the tool’s setup and test-cut procedure. Stop for binding, looseness, damage, burning or abnormal vibration.
Capture the information a model search cannot guess
Keep this checklist with your inspection or comparison. Checking a box only records that you have collected the item; it does not certify the bearing.
0 of 4 information groups recorded.
Technical basis & editorial scope
Original BearingScope workflow, written for catalogue research and comparison. Manufacturer material is used to check principles, not copied as a product endorsement or substituted for model-specific instructions. Reviewed 1 October 2026.
- CMT 2026 accessories and spare parts catalogue, printed page 436 (PDF page 41) — Exact series and edition only. Archived primary source or explicitly labelled factual extract; not an OEM interchange approval.
- CMT 791 bearing range, US and Canada web table — Exact series and edition only. Archived primary source or explicitly labelled factual extract; not an OEM interchange approval.
- Whiteside template-bit family table, including 3000 and 3000A — Exact series and edition only. Archived primary source or explicitly labelled factual extract; not an OEM interchange approval.
- Whiteside B9 and bearing size table — Exact series and edition only. Archived primary source or explicitly labelled factual extract; not an OEM interchange approval.
- Freud 62-series replacement bearing product records embedded in the 62-108 page — Exact series and edition only. Archived primary source or explicitly labelled factual extract; not an OEM interchange approval.
- Freud 32-504 rabbeting set: exact product specification — Exact series and edition only. Archived primary source or explicitly labelled factual extract; not an OEM interchange approval.
- CMT 7/8/935.001 rabbeting sets and bearing kits — Exact series and edition only. Archived primary source or explicitly labelled factual extract; not an OEM interchange approval.
- CMT 190/191/192B double-bearing spiral flush-trim range — Exact series and edition only. Archived primary source or explicitly labelled factual extract; not an OEM interchange approval.
- CMT 7/851B bowl and tray router bits — Exact series and edition only. Archived primary source or explicitly labelled factual extract; not an OEM interchange approval.
Source addresses and collection status are retained in the internal audit. No unpublished dimensions, torque settings, service intervals or interchange approvals are inferred.