Front radius arms width

Ive searched and managed to find out theres two widths of radius arm/bush 50/54mm, what i cant find out is there any difference to the arm at the chassis end?
Reason i ask as my radius arm bolts keep working loose, after finding out the bush width info i measured mine to find its a 54mm wide axle with 50mm wide arms! hence the bolts keep coming loose as theres not enough contact area.
Or can i just fit a washer each side of the 50mm arm bush hole as a cheap fix, not that im tight you understand!

Ta
Lynall

chassis end will be the same ,you can either change arms to suit or fit 2mm washers either side of bushes ,200 tdi and pre defender front axles used narrower arms 300 on used the same as disco