Headstock bearings 1948 Big 4

Previously wrote:

I was always told that ball races must have an odd number of bearings. Anyway, the book lists Part No. A2/521 - a set of 34 balls required for the head race, i.e. 2 sets of 17 each. They are a reasonably tight fit.

While we are on the subject, can anyone help with an associated question about the ball races available on these singles? I see more than one listed:-

B2/173 - Fork Crown or Head Clip Ballrace

A2/519 - Head Race - top

A2/520 - Head Race - bottom

What do top and bottom mean? Do they mean:-

(1) The upper and lower half of one ball race with 17 balls between them?

or

(2) The ball race (both halves), one at the top of the steering stem and another one at the bottom of it?

Why is A2/521 a set of 34 balls referring to both ends of the steering head? You might expect two Part Nos., each referring to 17 balls at top and bottom?

I have a number of ball race halves lying around and I am not sure which to fit where. They differ, but not by much,in the depth of the race. Does it even matter? By the way, all the external and internal diameters are the same and they all take 17 balls.

I am confused (not for the first time, many would say .....)

Thanks Chris, could not find reference to part nos quantities,just found that 17 balls top and bottom fitted exactly snug, but on setting adjustment of bearings found that i had slight play still present, and do remember in some old book a gap had to be left in the bearing race!