Due to the aluminium shortage Triumph used steel for the 3HW chain cases from early 1942,the photo below shows the inner and outer cases plus the spacers two for the chain cases and one that fits between the rear engine plates. 
The inner case has a large stepped washer held in place by a spring plate riveted to the chain case,this allows the washer to slide when the primary chain is adjusted,the stepped washer faces inward as shown and stops the clutch rubbing on the back of the case,and also stops the curved steel guttering from being damaged,this steel guttering is spot welded on,add diverts oil away from behind the clutch to help avoid leaks from there,the pipe in the middle of the case is the breather pipe. 
There is also an oiler for the rear chain,a small screw is undone and drips of oil lubricate the chain,the spacers are also shown. 
The chaincase oil filler plug was also made from steel to save on aluminium 
The rear of the chaincase has the battery carrier bracket spot welded on,the holes in the battery carrier base are in a different position than some Triumph models fitted with the aluminium chaincases. 
Machines fitted the pressed steel in place of aluminium chain cases were fitted with a cased felt washer between the two drive side bearings plus a distance sleeve which keeps the two bearings apart,the photo shows NOS ones,these are now unobtainable,when the engine on my 3HW was rebuilt this part was not refitted,but the new outer bearing was a rubber sealed type one rubber was prised out (inner one)and it has run like that for nearly twenty years,so I would say it is not needed (the distance sleeve is though).I don't know the reason why it was fitted in the first place but was used on the steel chain case only. 