Headset Bearing diameter - Is 42 really 41.8?

[FastforaSlowGuy]

I'm sourcing a new headset for an old CAAD frame, which takes the Campy-style headset bearings, which are 41.8 and 45*. A lot of headsets out there use 45* bearings and list their OD as 42. Is that an actual measurement, or is the market using 42 as shorthand for 41.8?

[Mark McM]

Originally Posted by FastforaSlowGuy

I'm sourcing a new headset for an old CAAD frame, which takes the Campy-style headset bearings, which are 41.8 and 45*. A lot of headsets out there use 45* bearings and list their OD as 42. Is that an actual measurement, or is the market using 42 as shorthand for 41.8?

42mm is the nominal size of the bearing. Because it is intended to be a slip fit, the bearing is slightly undersized. Here's a drawing of a FSA headset, showing that the top bearing is 41.8mm, to fit into a headtube bore of 42.0 +.1/-0.0.





Just last week there was thread about a press-fit crown race, where it was discussed that that the nominal size 30mm crown race was intentionally undersized (to ensure an interference fit). Depending on fit requirements, parts are frequently and intentionally made under or over their nominal sizes.

[ultraman6970]

Probably the bearing is a cane creek spec and not a campagnolo one.

The cane creek bearing is tad smaller but one of the sides is 45 degrees the other one is 36 degrees. those are like 41.5 OD Sometimes is hard to read the numbers.

[Velocipede]

Originally Posted by FastforaSlowGuy

I'm sourcing a new headset for an old CAAD frame, which takes the Campy-style headset bearings, which are 41.8 and 45*. A lot of headsets out there use 45* bearings and list their OD as 42. Is that an actual measurement, or is the market using 42 as shorthand for 41.8?

Originally Posted by ultraman6970

Probably the bearing is a cane creek spec and not a campagnolo one.

The cane creek bearing is tad smaller but one of the sides is 45 degrees the other one is 36 degrees. those are like 41.5 OD Sometimes is hard to read the numbers.

The 42mm headset bearing is really 41.8mm as Mark mentioned. It's a very common size on tapered headtubes. It was invented by Columbus and is considered the "Italian" headset. It's been associated with Campy because they were used on the Columbus frames most. But Columbus has been using this since they came out with an integrated headset headtube. The standard headset bearing for an integrated is a 41.0mm. Most headset companies make both a 41.0 and 41.8mm bearing. But companies call them 42mm bearings cause that's what they fit.