Oval backplate stub axles.

[Robert Foreman]

I'm refurbishing an axle with oval backplate stubs. On removing the old kingpin bushes I noticed that the top and bottom bushes have different outside diameters. The top bush is 11/16" Od and the bottom 41/64".
   Every other axle I have rebuilt both bushes are 11/16". Is this a peculiarity of the oval backplate type?

[bystander]

Yes.

Top bush o.d. is as the earlier type, bottom bush o.d. is as the later semi-Girling type (but it's the length of the earlier type)

[Tony Press]

Back in July 2020 I asked: 

Can one of our experts advise the correct outside diameter of the standard King Pin Bushes  BL 7 and BL 8 
The size measured from old bushes-  
Lower flanged Bush BL 7: OD 16.2 mm (41/64" ?) 
Upper plain Bush BL 8: OD 17.40 mm (11/16" ?) 

Measuring our Club stock bushes 
Lower flanged bush 17.46 mm
Lower flanged bush16.20 mm
Upper plain bush 17.44 mm
 
There was no reply to my question so I took the dimensions to be: 
Lower flanged Bush BL 7  OD 16.2 mm (41/64")  
Upper plain Bush BL 8   OD 17.40 mm (11/16") 
 
Now from the above comments it appears that BL7 and BL8 should both be

Upper and lower Bush BL 7 and BL 8: OD 17.40 mm (11/16") 

During 1936, with the new stub axles the bushes became:
Lower flanged Bush 1A4129 OD 16.2 mm (41/64")  
Upper plain Bush 1A4128  OD 17.40 mm (11/16") 

 Is this correct ?

[Robert Foreman]

Thanks for the reply bystander,
I wonder why they made the bottom bush a smaller outside diameter?