3M 5541 4" Roloc Disc Pad Holder. Backup pad designed to support 3M Roloc 4" diameter abrasive discs. This pad has a 1/4-20 INT thread which allows it to be mounted directly to tools with 1/4-20 EXT threaded shafts. Assembly also includes a Roloc shank and adaptor.
3M - Scotch 8883643577