The Union Butterfield 1587(UNC)/1587(UNF)/1588(UNC)/1588(UNF) uncoated, high-speed steel spiral flute tap has a round shank with a square end and a high-helix design, and is used to create right-hand threads in a range of materials with strength in brass, bronze, aluminum and unalloyed magnesium. It is available in two different ANSI thread specification standards: UNC (Unified Coarse) and UNF (Unified Fine). The spiral flutes of this tap pull chips back from the tip of the tool, up and out the hole to prevent clogging; the higher helix angle (52 degrees) further improves chip removal. These characteristics make the tap suitable for blind or bottoming holes .
Right-hand threads are designed to tighten when a head or nut is rotated clockwise (the most common threading direction). High-speed steel (HSS) is a common general-purpose steel for cutting tools and is compatible with a variety of materials. With no coating or surface treatment, this uncoated tool can be used on a broad range of materials and provides an economical alternative to coated tools. The round shank with square end helps to minimize rotation in the tool holder. This tool can be used in machines, such as drill presses or lathes, or with hand tools such as tap wrenches.
In the Union Butterfield 1587(UNC)/1587(UNF) series, taps with machine-screw sizes of 3 to 6 have two flutes, and machine-screw sizes 8 to 12 have three flutes. In the 1588(UNC)/1588(UNF) series, all taps have three flutes. In both series taps are available with a variety of chamfers. This tap conforms to ANSI standards and can create threads to a depth 2 ½ times its diameter. The 1588(UNC)/1588(UNF) series tap is suitable for ANSI 2B and 3B tolerance classes: 2B is an average quality fit for commercial and industrial fasteners; 3B produces close-tolerance fasteners that resist loosening, as in aerospace applications. The 1587(UNC)/1587(UNF) series tap is suitable for the ANSI 3B tolerance class.
Taps produce internal threads in previously formed holes and can be used in machines (such as drill presses) or with hand tools. Common types of taps include hand taps, spiral point taps, spiral flute taps, thread forming taps, and pipe taps. Hand taps (straight-flute taps) collect chips in the straight flutes of the tool; spiral point taps push chips through holes ahead of the tool; and spiral flute taps pull chips back from the tip of the tool, up and out the hole. Thread forming taps, also known as cold forming taps, press rather than cut to create threads in a drilled hole, and no chips are created. Pipe taps create threads in pipes and pipe fittings. Each thread type designates a thread profile and each type is identified with an abbreviation. In the U.S. and Canada, the Unified Thread Standard is the dominant thread type, including UNC (Unified Coarse), UNF (Unified Fine), and NPT (National Pipe Taper) threads, among others.