taper-bush
Technical Knowledge
QD bushings are identified by lettered families rather than the numbered Taper Lock series. That naming system is useful because the letter fixes the outside flange/barrel geometry; the shaft bore and keyway are then selected within the family. For replacement, both pieces of information matter.
The table below is a quick dimensional reference for EP-SF through EP-S standard QD family sizes. Use it with the drawing, because bolt circle, cap-screw arrangement, bore range and standard/shallow keyway options are also part of the interface.
QD designation system
The QD sequence progresses through lettered sizes as the bushing grows. The steel QD range includes EP-SF, EP-E, EP-F, EP-J, EP-M and EP-N; larger standard-family references include EP-P, EP-W and EP-S. The model letter identifies the mating hub family, not a single shaft diameter.
SF to S dimension reference
| EP QD family | A (in) | B (in) | D (in) | Approx. weight (lb) |
|---|---|---|---|---|
| EP-SF | 9/16 | 3.125 | 4 5/8 | 3 |
| EP-E | 3/4 | 3.834 | 6 | 10 |
| EP-F | 13/16 | 4.437 | 6 5/8 | 11.5 |
| EP-J | 1 | 5.148 | 7 1/4 | 18 |
| EP-M | 1 1/4 | 6.500 | 9 | 37 |
| EP-N | 1 1/2 | 7.000 | 10 | 57 |
| EP-P | 1 3/4 | 8.250 | 11 3/4 | 120 |
| EP-W | 2 | 10.437 | 15 | 250 |
| EP-S | 3 1/4 | 12.125 | 17 3/4 | 400 |
Bore range and keyway options
The QD technical sheet includes stock-bore ranges and distinguishes standard and shallow keyway configurations. When an old QD bushing is being replaced, record the letter family, bore, keyway type and mating sheave/sprocket. A bushing with the correct bore but the wrong QD family will not match the outside hub geometry.
Plain bore and stainless options
The technical data also includes plain-bore/not-split references and notes that stainless-steel QD bushings can be made to order. Treat these as separate configurations that need explicit RFQ details; do not assume a standard split steel QD bushing and a special plain or stainless version share every feature.
Selecting the right QD series
For replacement, identify the installed QD family first from marking, flange dimensions and bolt circle, then match the shaft bore/keyway. For a new fabricated component, choose the QD size with the hub or weld-on hub design, then make sure the shaft and duty can be supported by the complete assembly.
Frequently asked questions
Does EP-SF mean one fixed shaft bore?
No. The QD family fixes the outside interface; different shaft bore and keyway configurations can exist within the family.
What is a shallow keyway option?
It is a distinct keyway configuration shown in the QD technical data. Specify standard or shallow when matching an existing shaft.
Related products and resources
Need help with a real application?
Send the model, shaft diameter, keyway or drawing so the enquiry can be checked against the correct bushing family.