8

The Park Tool website has a page describing the standardized headset identification system.

I would like to confirm that I've understood it properly. Is this bottom section of a press-fit headset shown in the picture a ZS56/40?

NOTE: I've taken measurements with inexpensive digital calipers and the fractional component of the value can change significantly depending on how much force is applied when turning the thumbwheel.

lower press-fit headset section

1 Answer 1

7

Yes ZS56/40 - Zero stack with 56 mm bore diameter and 40 mm fork crown race.

It is zero stack because it is a black cup containing the silver bearing, but the bearing ends up inside the frame tube (i.e. not external). The 56.10 mm dimension gives a snug interference fit with a 56 mm head tube ( bore diameter). The 39.95 or so is about the 40 mm dimension that interfaces with the crown race/steerer tube. That last measurement seems slightly tight but possibly measurement error, tolerances aside it would be called a 40 mm.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.