Guide · Router and spindle mounts
How to measure a router or spindle body for a mount
Where to put the caliper on a router or spindle, how to record the reading, and why makers' size labels round and sometimes disagree.
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Short answer
Measure the round clamping band where the holder grips the motor, with a caliper, at two or three angles. Write the number in millimeters, then compare it with the size the mount maker names for your router or spindle. Labels round, and two makers can label the same router differently, so the maker's named fit decides.
Where to measure
Measure the plain cylindrical band the mount clamps onto. That is the body diameter a mount bore is sized for. Do not measure the motor cap, the vent ring, the speed dial housing or the router's base.
- Unplug the router or spindle, or take it off the machine.
- Wipe the band clean.
- Close the caliper jaws square across the band and read the number.
- Turn the motor about a third of a turn and read again. Repeat once more.
- Record every reading, not just the one you like.
If your readings disagree by more than the last digit, the band may be dirty, tapered or not round. Measure again at the same height before you order.
Inches and millimeters
One inch is exactly 25.4 mm.[1] If your caliper reads in inches, multiply by 25.4. A conversion is a calculation, not proof of fit.
Labels are rounded
A body labeled for one size is not always exactly that size. Sienci gives its AutoSpin body as 64.8 mm and says it fits 65 mm router mounts.[2] That is Sienci's statement about its own spindle, not a general rule about how close is close enough. Carbide 3D gives its Compact Router a 65 mm body.[3]
We found no published fit tolerance from any mount maker in our sources. If your reading sits between two sizes, ask the mount maker before you buy.
Makers label the same router differently
FoxAlien sells its Z clamp in 65 mm for routers like the Makita RT0701C and 69 mm for routers like the DeWalt DWP611.[4] Sienci lists its 71 mm LongMill mount for the DeWalt DWP611 and the Bosch Colt.[5] Neither maker explains the difference. Our DeWalt DWP611 69 or 71 mm guide shows both labels side by side.
Sienci's LongMill mount comes in 52, 65, 71 and 80 mm sizes.[5] So within one maker, the label you need follows the motor you own.
A listing can contradict itself
The Genmitsu DS52 dust shoe page gives the spindle diameter as 52 mm (1.65 in) in its text and 52 mm (2.05 in) in its spec table.[6] 52 mm works out to about 2.05 in, so trust the metric figure and treat the other as a listing error.
Mount body vs bore
A mount has two sizes: its bore (what it holds) and its outside body (how it bolts on). PwnCNC offers its Spindle Mount with a 65 mm or 80 mm bore, and both share the same external dimensions.[7] When you replace a mount, check both.
Caliper accuracy
Mitutoyo publishes a bulletin on the accuracy and calibration of digital, dial and vernier calipers, based on ASME B89.1.14-2018.[8] Read it if you want to know how calipers are checked. We do not quote accuracy values from it here.
Your measuring sheet
| Field | Yours |
|---|---|
| Motor maker and model | |
| Reading 1 (mm) | |
| Reading 2, turned (mm) | |
| Reading 3, turned (mm) | |
| Size the motor maker states | |
| Size the mount maker names for this motor | |
| Current mount bore |
Once you have a size, buy the holder whose maker names that bore for your machine. Genmitsu sells its 4040-PRO family holder in two bores:
Picks that fit2 products
Choose the 65 mm holder (101-63-ZC65) for Makita RT0700C-class bodies and the 69 mm holder (101-63-ZC69) for DeWalt DWP611-class bodies; Genmitsu lists both for the 4040-PRO, 4040-PRO MAX, 4040 Reno, 3020-PRO Ultra and 3030-PROVer MAX.
65 mm holder for the Genmitsu 4040-PRO family
Genmitsu 65 mm aluminum spindle holder (101‑63‑ZC65) for the 4040‑PRO family
69 mm holder for the Genmitsu 4040-PRO family
Genmitsu 69 mm aluminum spindle holder (101‑63‑ZC69) for the 4040‑PRO family
Next
Questions
Where on the router do I measure?
On the plain round band the mount clamps onto, not the motor cap, vent ring or base. Take two or three readings, turning the motor between them.
What if my reading is between 65 and 69 mm?
Measure again on a clean band, then compare with the size the motor's maker and the mount's maker state. We found no published fit tolerance, so if it still sits between sizes, ask the mount maker before ordering.
Is a 64.8 mm body a 65 mm fit?
For Sienci's AutoSpin, Sienci says so: it gives the body as 64.8 mm and says it fits 65 mm router mounts. That is Sienci's statement about its own spindle, not a rule for other motors.[2]
My caliper reads in inches. How do I convert?
Multiply by 25.4: one inch is exactly 25.4 mm. The result is a calculation, not proof that a metric mount fits.[1]