Legend:
b - length of the thread (at least)
l - length of bolt
d - the nominal diameter of the thread
k - head height
r - radius
e - the diameter of the circumscribed circle (not less than)
s - size hex head turnkey
c - thickness of the mounting collar
ds - diameter of the screw shank
u - thread run
lg - length of the shank to thread
ls - length of the shank to the start of the thread
da - the maximum diameter of the stem at the head of the screw
dw - minimum diameter of the seat
k´ - minimum size of the head on the key