Exact dimensions of studless Technic beams
Technic, Liftarm 5 x 7 Open Center Thick


Height = 7.86mm
Width = 39.80mm
Length = 55.85mm
Opening width = 24.08mm
Opening length = 40.20mm


Technic, Liftarm 1 x 9 Thick (oriented as shown on Bricklink image):


Height = 7.86mm
Width = 7.44mm
Length = 71.36mm


(measured with digital caliper, precision +/-0.05mm)