here i have a mystery vintage bike exhaust tightening collar that is made from some form of alloy ie - brass \ bronze etc.etc.
as can be easily sen from the 3 images - 2 of the small fins have been drilled this will have been done for securing with wire, possibly when racing many road bikes had this modification carried out !
also some of the fins are slightly bent over, this will have been caused by hitting them to tighten them up..
also at the top end of the threads there is a saw cut mark, as this damage is at the top it may not cause any problems..
the internal diameter is 42.5mm.
if you know as to what this exhaust ring fits please let me know !!
many thanks dave