Guide · Insert and reducer rings
Which ring opening for your bit diameter: what makers say
Pick the smallest ring that clears your bit by your ring maker's margin. Woodpeckers and Bosch give different rules; here is each one, with the openings each set offers.
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Short answer
Pick the smallest ring in your plate's system whose opening clears the bit's cutting diameter by the margin your ring maker gives. Makers give different rules: Woodpeckers suggests an opening about 1/8 to 1/4 in larger than the bit, and Bosch says at least 1/16 in per side on its RA1181. Use your own maker's figure.
Start with the system, then the opening
A ring only helps if it fits your plate. Rings belong to one plate or lift system, so first confirm whether yours is Level-Loc, Twist Lock, Tab-Lock, MagnaLOCK or another system; our ring systems guide shows how. Then choose the opening.
On this page a router bit appears only as a diameter: the widest part of its cutting edge, which the ring's opening must clear. We give no bit or speed advice; follow the bit maker's instructions for that.
Woodpeckers: about 1/8 to 1/4 in larger than the bit
Woodpeckers recommends a router bit opening about 1/8 in to 1/4 in larger than the bit diameter when choosing among its Twist Lock rings.[1] That is Woodpeckers' advice for its own rings. It is not a rule for other makers' rings.
Example: for a bit with a 1-1/2 in cutting diameter, that advice points to an opening of roughly 1-5/8 to 1-3/4 in. In the Woodpeckers TLRSET-ML set, the 1-5/8 in ring is the smallest that falls in that band.
Bosch RA1181: at least 1/16 in per side
Bosch's RA1181 manual says to match the bit's cutting diameter to the ring's inner diameter so that the difference is no less than 1/16 in on a side, and not to alter the insert ring or the plate's bit hole.[2]
Bosch also says which bit sizes go with each of the three rings supplied with the RA1181:[2]
| RA1181 ring hole | Bosch's bit limit |
|---|---|
| 1 in | Bits up to 7/8 in |
| 2 in | Bits up to 1-7/8 in |
| 2-3/4 in | Bits up to 2-5/8 in |
| No ring | Bits over 2-5/8 in up to 3-1/2 in |
Bosch says not to use the table with bits over 3-1/2 in in diameter, because they exceed the clearance hole in the tabletop insert rings.[2]
The openings each system offers
The add-on sets below are where most readers find an in-between size. Full contents, including the rings supplied with each plate, are in the insert ring set sizes lookup.
| Set | System | Openings the maker lists |
|---|---|---|
| Kreg PRS3050 | Level-Loc | 3/4, 1-3/8, 1-5/8 and 2-1/8 in, plus a blank ring[3] |
| INCRA MLRINGSET-3.5 | MagnaLOCK | 3/8, 5/8, 7/8, 1-3/8, 1-5/8, 1-7/8, 2-5/8 and 3-3/8 in[4] |
| JessEm 8-piece Tab-Lock | Tab-Lock | 3/8, 1/2, 3/4, 1, 1-1/4, 1-1/2, 1-3/4 and 2-1/4 in[5] |
| Woodpeckers TLRSET-ML | Twist Lock | Solid, 3/4, 7/8, 1-3/8, 1-5/8, 1-7/8, 2-1/8 and 2-3/8 in[1] |
Working it out for your bit
- Measure or read the bit's largest cutting diameter from the bit maker's listing.
- Find your ring maker's clearance rule in its manual or product page.
- Add that margin and pick the smallest ring in your system that is at least that large.
- If no ring is large enough, use the plate maker's own guidance for larger bits. Do not cut or file a ring unless the maker's instructions cover it.
If your ring maker publishes no rule, ask the maker. Do not borrow another maker's figure as if it were universal.
Can I enlarge a ring?
Bosch says not to alter the RA1181's rings or plate hole.[2] Kreg sells a blank Level-Loc ring for making a custom opening.[3] We give no cutting or drilling steps; follow the maker's instructions.
Ring sets for a named system
Picks that fit2 products
Kreg PRS3050 (3/4, 1-3/8, 1-5/8 and 2-1/8 in plus a blank): Kreg Level-Loc plates and the Kreg PRS5000 lift only.
More on choosing
Woodpeckers TLRSET-ML (solid plus seven openings from 3/4 to 2-3/8 in): Woodpeckers Twist Lock plates and lifts only. On Amazon, check that Ships from / Sold by is Amazon.com or the brand.
Kreg Level-Loc plates and lift
Woodpeckers Twist Lock plates and lifts
Next
Questions
What size insert ring do I need for my bit?
The smallest ring in your plate's system whose opening clears the bit's cutting diameter by your ring maker's margin. Woodpeckers suggests about 1/8 to 1/4 in larger than the bit for its rings; Bosch says at least 1/16 in per side on the RA1181.[1][2]
How much clearance should a ring have around the bit?
Use your own ring maker's figure. There is no single rule across makers: Woodpeckers and Bosch publish different ones, each for its own rings or table.[1][2]
Can I enlarge a ring opening?
Bosch's RA1181 manual says not to alter the insert ring or the plate's bit hole. For other plates, follow that maker's instructions; Kreg sells a blank ring for a custom opening, but we give no cutting steps.[2][3]
What do I use for a bit larger than my biggest ring?
On the Bosch RA1181, Bosch says to use no ring for bits over 2-5/8 up to 3-1/2 in, and never to use bits over 3-1/2 in on that table. On other tables, check the plate maker's largest stated opening and its limit.[2]