This is a flat #0 Horseman field lensboard (80 X 80mm) which allows for mounting lenses in Copal/Compur #0 shutters. This lensboard fits all Horseman folding bed metal field cameras(VH, 45FA, 45HD etc).
NOTE: Horseman FA, HD and VH will only accept lenses with a rear diameter of 2.5" (63mm) or less!