Ok, I've got the stock Technics, a pair of Revox, and a pair of Teac 10.5" hub adapters. When I put each of these on an aluminum 10.5" reel, they are all flush with the inner side of the reel. I measured a plastic 7" reel ( that I have used for years as a take-up reel on several machines with no rubbing ) and the metal 10.5". The overall thickness is the same. The inner space ( where the tape goes ) isn't. The plastic reel is 8mm and the metal 9-10mm ( it's been around the block). So, obviously, the metal is thinner. So that would only give the metal reel moreclearance. So, I took a straight edge and took a look at the reel turntables. You know, it has that rubbery pad on it with the 6 raised disks around the pin and then a raised ring at its border. The raised disks and ring are flush with each other. When the 7" reel is on, it rests on the disks and the ring. Same with the metal reel but less on the disks. But, since the disks and the rings are at the same height, it shouldn't matter. So, why the spacers?