Diameter 3"/80mm, Aluminum base, Nylon backer, M10 M14 Thread ; Packaging includes : 1PC . Aluminum body providelonger working life and can bear heavy duty workingas steel body but lighter weight . Note:Backer's max capacity is 5000RPM,Please don't use it with high speed grinder/polisher,recommended speed is 2500RPM . Backer for diamond polishing pads, sanding disc, and grinding discs . All aluminum alloy,Strong adhesion point.Durable and long-lasting.Safe and sturdy ., Manufacturer: HMVFXBUDK