T51 Quick Change Tool Set. Quick change tool post for lathes. The set comes with 4 standard holders, 1 parting holder and 1 Boring Holder. The main block is 3″ square by 2″ high with a 5/8 bore. 1 mounting block 72 x 72 x 51mm. All the parts are hardened and ground. We ensure the product reaches you at the earliest.