Fra http://www.skgrimes.com/lensboards/index.htm finner jeg:

"Technika 4x5
3.868 x 3.773, cast aluminum. Double circular light lip (3.45 and 3.39) loacted on the rear, off-center of the lens board. Edge thickness is .075. Bottom corners cut at an angle and a notch present in the center. Original Technika boards have the shutter hole located off-center in the light lip to align the center of the lens with the film plane. (Approx. 5mm - 6mm down). Other brands use the center of the light lip as the shutter location."

Tykkelsen er altså 1,9mm, mens jeg mangler tykkelsen på de runde lysfellene.