Waltham Balance Staffs 1364 vs 1365

The difference between these two staffs appears to be the size of the "waist". What area of the staff is being referred to? Is the waist the hairspring shoulder?....or the balance hub?

The waist is what fits in the balance wheel . ..When you see large or small collet listed on staffs that,s the part of the staff where the hairspring fits.

OK...I think I "got it".....the waist appears to be the largest dia. of the HUB of a BS....but....consider the following. My research into the difference between these 2 staffs is....the 1364 is a longer and fatter staff. The so called "waist" has little to do with the function, repair, or installation of these staffs.....Consider...

The 1364 has a total lenght from pivot to pivot of......5.85mm
The 1365 has a total lenght of..........................5.84mm

The 1364 has a balance wheel shoulder dia of............1.25mm
The 1365 has a balance shoulder of......................1.23mm

The 1364 has a roller post (Largest Dia.) of............0.62mm
The 1365 ...............................................0.61mm

The 1364 has a hairspring shoulder dia..................0.92mm
The 1365 ...............................................0.91mm

So.....some describe these 2 staffs as the same except one has
a large "waist" and the other has a small "waist". It appears
the "waist" size has nothing to do with the function and operation
of either staff, in a Waltham 18s SN 1751889. Further...it appears, over
time, these two staffs have been mixed up while in stock of several
PW parts suppliers. I have ordered the 1364 form 3 different
suppliers...only one supplier has sent the correct staff. Anybody out there have a 1364 that will meet or exceed these specs? I can make a BS
smaller....but...I do not know how to make a balance staff larger.
ctonyzee@netlabs.net