DIN 792

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

ddkktfb
M 24382512.16.654
M 30483015.66.666
M 33523016.47.672
M 36583518.28.678
M 39624019.98.684
M 42684022.68.690