Measured with calipers in the frame openings just now
Singer Graflex RH10 58.0 by 67.7
Older Graflex RH/8 57.4 by 77.7
1936 Nettar 56.5 by 85.2

The RH/10 is for the 2 x 3 Graflex
The RH/8 is for the 4 x 5 Graflex