Thread Sizse: 1/4″ 5/16″ 3/8″ 7/16″ 1/2″, M5 M6 M8 M10 M12. M12 x 1.75 + Tool Kit 10PC Inserts √. M5 x 0.8 + Tool Kit 25PC Inserts √. The installation tools in this kit are made of high speed steel for excellent handling, while the inserts are stainless steel for increased strength and longevity.