Hi Charlie, the pic shows them back to back, I've got mine shimmed on the OD (as you want the tightening to pull the inner races together and load the bearings slightly) and cut the shims out of ali cans (good source of 0.1mm thick shim material as well as providing refreshment!) with some sharp scissors for the OD and a stanley knife for the ID. Think I used 2 or 3 shims per BK support but can't remember now.