McGuire Glossary of Fastener Terminology

1 - 7 terms

12 POINT FLANGE HEAD - Double hex, 24 flats with an integral formed circular collar connected to the base of the double hex. Top surface may be flat or indented.

12 SPLINE HEAD - 12 splines centered at 30 degrees increments around the outer circumference of the head and are parallel to the axis of the fastener.

12-POINT DRIVE - A 12-Point screw drive uses two overlapped hexagon shapes, one rotated by 30 degrees. Standard 12-Point hex socket bits and wrenches fit these screws. The screw heads are typically flanged, and may fit into standard Allen hex socket cap screws counterbores molded or machined into pats to be fastened.

12-SPLINE DRIVE - The 12-SPLINE drive has 12 splines in the fastener and tool. It consists of 12 equally spaced protrusions, each with a 60 degree angle. It is achieved overlaying 4 equilateral triangles, each one rotated 30 degrees over the previous one. Its primary advantage is its ability to resist cam out, so it is used in high-torque applications.

12-UN SERIES - A standard diameter-pitch combination with medium-pitch threads and 12 threads per inch. This series is commonly used instead of UNF threads for dolt diameters of 1 1/2 inch.

16-UN SERIES - A standard diameter-pitch combination with coarse-thread-pitch thread and 8 threads per inch. This series is commonly used instead of UNC threads for bolt diameters over 1 inch.

18-8 - Stainless Steel with 18% Chrome and 8% Nickel approximately. The term "18-8" (300 Series Stainless) is used interchangeably to characterize fasteners made of 302, 302HQ, 303,304, 305, 384, XM7, and other variables of these grades with close chemical compositions. There is little overall difference in corrosion resistance among the 18-8 types, but slight difference in chemical composition do make certain grades more resistant than others against particular chemicals or atmospheres. "18-8" has superior corrosion resistance to 400 series stainless, is generally non-magnetic, and is hardenable only by cold working.