Overlap Length = CH + BH + T - SH

Where CH = Cover Hook
BH = Body Hook
*T = Cover Plate Thickness
SH = Seam Height (Width or Length)
* In general practice, .010” may be used for the cover thickness. However for accuracy, the actual plate thickness of the cover should be used.

Calculation of percent overlap:
Overlap, % = 100 x (BH + CH + T - SH)/[SH - ((2 x T) + BPT)]

Where BH = body hook length
CH = cover hook length
T = cover plate thickness
SH = Seam Height
BPT = Body Plate Thickness
Use minimum value found for reach measurement (maximum value for SH)

Percent Body Hook Butting
Calculation: (A / B) x 100

Where A = Body hook butting (length of body hook in contact with the cover hook)
B = Total body hook length

It is recommended that both overlap and body hook butting be optically measured.