Image 1 of 2 Image 2 of 2 Direct Thread Adapters- 17-4 Stainless Steel $59.00 HUB (1.375-24 TPI)- direct thread adapters. Made from 17-4SS, designed to work flawlessly without suppressors. Thread Size: Select Thread Size 1/2-28 1/2-36 5/8-24 .578-28 3/4-24 3/4-28 Quantity: Add To Cart Added! HUB (1.375-24 TPI)- direct thread adapters. Made from 17-4SS, designed to work flawlessly without suppressors.