ITEM NAME:180 Set Leather Rivets Double Cap Rivet Tubular Metal with Tool Studs Fixin H8M4 Description&Preview.There are groove on the base tool that can fix rivet and prevent rivet knocking bending and sliding, the base one side groove size is 8 mm and another side is 6 mm. 30 x 8 mm silver rivets. 30 x 6 mm silver rivets.