pin is a device used for fastening objects or material together. Pins often have two components: a long body and sharp tip made of steel, or occasionally copper or brass, and a larger head often made of plastic. The sharpened body penetrates the material, while the larger head provides a driving surface. It is formed by drawing out a thin wire, sharpening the tip, and adding a head. Nails are related, but are typically larger. In machines and engineering, pins are commonly used as pivots, hinges, shafts, jigs, and fixtures to locate or hold parts.

Straight pins
Pin typeTypical sizeTypical length
Beading pins147⁄8 in (22 mm)
T-pins0.75 mm1 1⁄4 in (32 mm)
Dressmaker pins17-201 1⁄16 in (27 mm)
Pleating pins171 1⁄16 in (27 mm)
Applique pins0.6 mm3⁄4 in (19 mm)
Bridal and lace pins171 1⁄4 in (32 mm)
Patchwork pins22 (0.5 mm)1 7⁄16 in (37 mm)
Quilting pins30 (0.6 mm)1 7⁄8 in (48 mm)
Silk pins0.5 mm1 7⁄16 in (37 mm)
Pearlized pins241 1⁄2 in (38 mm)
Sequin pins8 (0.5 mm)1⁄2 in (13 mm)
Tidy pins-1 1⁄2 in (38 mm)
Hatpins-8 in (20 cm)

Above info is from the reference.