b - length of the thread (at least)
d - the nominal diameter of the thread
k - head height
dk - head diameter
f - width of the nib
t - length of the nose

DIN 792 Dimensions for Cylindrical Head Nib Bolts

d	dk	k	t	f	b
M 24	38	25	12,1	6,6	54
M 30	48	30	15,6	6,6	66
M 33	52	30	16,4	7,6	72
M 36	58	35	18,2	8,6	78
M 39	62	40	19,9	8,6	84
M 42	68	40	22,6	8,6	90