after may 19, 1986 several manufacturers were modifying receivers so sears and conversion parts would fit and run. eventually BATF decided these mods were "making a MG" those already done were permanently married and no new were allowed. relieving the trunion on a mini or micro receiver is not allowed, and is considered "making". the micro does have space on either side of trunion at bottom, so modified feet can slide under. A mini registered bolt can have feet cut down to a point they will slide under the Micro trunion and work. The working issue is whether the bolt has enough "running start" to strip ammo from mag and push it into the chamber, otherwise you are faced with the problems of the no feet bolt-- see in library under mini & micro full auto conversion sections. there are no pics of the micro trunion in the micro full auto conversion section, but the Bolts section in the Mini part will explain.