Each size comes in various lengthsShort (length same as the diameter of the bolt or screw for short thread engagement applications)Medium (length 1-1/2 times the diameter of the bolt or screw)-provides sufficient strength in most applicationsLong (length two times the diameter of the bolt or screw)-provides higher strength in critical applications, (especially in magnesium)Fastserv stocks a complete line of Perma-Coil? inserts and stainless steel inserts are for standard and spark plug repairPerma-Coil? is made in the USA and is 100% interchangeable with helicoilDiameter: #12 Drill Size: 15/64 Inch Drive Size: .216 Head Height Max: 15/64 Item: Perma-Coil? Thread Repair Insert Length: 0.216 Inch Material: Stainless Steel Thread Size: #12 Thread Type: Coarse