Rear Axle Half Shaft Changes.

[Tony Press]

Just trying to work out two secondhand halfshafts. 
Both are less than 22.5" - more like 22 1/4".
Of this measurement, approx 3/4" is the thread, so they are 21.5" to the end of the contact area.

They have different finishing to the toothed end... the clean one is 0.86" diameter (just behind the teeth), and there is more chamfer on the inner circle pictured. The tarnished one with less chamfer is 0.87". Tony's early and late measurements equate to 0.87 and 0.89 of an inch for the two shafts.

The 2 diameters of SWB shaft are apparently not interchangeable. Is this just because of the diff case bush alone? 

I presume both mine are "earlies"? Is the changeover to the fatter shaft came in with the last incarnation of the swb axle type (type III in the green Companion picture, accepting type 4 is the D type)?

From the 1923 Spare Parts book 353a the early Axle Shafts were BO 17 (offside) with left hand thread and BO 18 (nearside) with right hand thread. No length given. 

By 1925 SP Book 353h there was only one Axle Shaft BO 18 listed.

The June 1931 SP List 670f shows a new Axle Shaft BO 128.

November 1933 SP List 1029A  shows another new Axle Shaft BO 136 , by September 1936 listed as 1A 7181.

Unfortunately the cards don't seem to show details of the Axle Shaft changes

Cheers, Tony.