40 Pin Female Header is a single row 40-holes female header. It can be cut to size with a pair of wire-cutters Standard-1 spacing. It is extensively used in the development boards. They mate very well with breakaway male headers.
Features of 40 Pin Female Header:

Receptacle Style: Square.
Number of Pins: 40.
Pin Spacing: 0.1? (2.54 mm).
Receptacle Depth: 6 mm.