By John Morris · September 17, 2026
“Will a 3.25-inch collet fit this lift?” combines two different parts of a router. The lift holds the motor body or supports the router base. The collet grips the router bit. Collet capacity cannot tell you whether a motor will fit a lift carriage.
Compare O'SKOOL RTS05 Router Lift for 3-1/2-Inch Motors
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O'SKOOL RTS05 Router Lift for 3-1/2-Inch Motors
O'SKOOL's RTS05 is an aluminum-plate lift listed for 3-1/2-inch router motors. Its fit claim concerns the motor, so the table opening still needs a separate check.
Check on AmazonThree measurements, three jobs
- Motor-body diameter
- The outside dimension of the cylindrical housing at the intended clamping area. This is relevant to a lift that clamps a removable motor.
- Collet size
- The shank size a particular installed collet is designed to hold. Follow the router and bit instructions rather than trying to close a mismatched collet around a shank.
- Plate dimensions
- The dimensions of the lift's tabletop plate. These describe the table interface, not the router interface.
Likewise, a horsepower number is a power designation, not a diameter. A reference to a 3¼-horsepower router should never be turned into a 3¼-inch mounting specification.
Measuring a removable motor
Disconnect power and use the router manufacturer's procedure to release the motor from its base. Measure only the intended cylindrical mounting surface with suitable measuring equipment. Do not include a raised label, control, protruding casting or the base itself. Record the units and retain the exact model identification alongside the measurement.
For unit conversion, 3.5 inches equals 88.9 millimeters. That mathematical equivalence does not prove that every housing advertised at either dimension is suitable for the same clamp. A motor also needs the correct shape and sufficient approved clamping area.
How manufacturers use diameter specifications
O'SKOOL describes the RTS07 as a system for 3½-inch motors and also publishes named supported models. JessEm's Rout-R-Lift 3.5XT similarly identifies supported motors, with a separate collar arrangement for certain smaller models. The named-model documentation is more useful than treating either diameter description as an unrestricted promise.
SpeTool's P01002 documentation illustrates another reason to avoid a diameter-only decision: its published imperial upper bounds are inconsistent. We use the manufacturer's named motor list rather than converting that inconsistency into a universal fit rule.
If your measurement is close but the model is absent
Send the lift manufacturer the complete model number and ask for the approved mounting configuration. Do not improvise packing material or tighten beyond the specified procedure to make a near match grip. Our compatibility sequence covers the remaining checks. Owners of smaller motors can also use the compact-router guide; table-opening measurements belong in plate sizing.
Write fractional inch measurements exactly as supplied. Rounding a nominal size for a shopping comparison is different from establishing a mechanical tolerance, which must come from the equipment documentation.
Explore O'SKOOL Router Lift for 4.2-Inch Motors
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O'SKOOL Router Lift for 4.2-Inch Motors
This O'SKOOL configuration is listed for 4.2-inch router motors. It serves a different motor class from the brand's 3-1/2-inch lifts and needs its own fit check.
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