This is the aluminium cast back bush that goes under the reel table and has a ridge in for a belt for the reel counter
it was from an A3440 but I am guessing this is a common part in several machines of that era, it does not appear
to be the same like in the newer machines but i have not seen them all and these may also be suitable, though I can say
for sure these came from the 3440 series.
This is in nearly all machines up to the 30 series which these still fit 28mm between holes on the reel table