An Etymological Dictionary of the German Language/Bolz
Bolz, Bolzen, m., ‘short arrow-bolt,’ from the equiv. MidHG. bolz, OHG. bolz, m.; comp. the equiv. OIc. bolte, AS. bolt, E. bolt; allied to Du. bout, ‘cramp-pin.’ The word has the same meaning in all dialects, and in all the various periods of the Teut. languages. We may assume a pre-Teut. bhḷdó-s, with the meaning ‘bolt, dart’; yet no such word outside the Teut. group can be adduced. Bolzen cannot be immediately akin to MidHG. boln, ‘to throw, hurl,’ since the Teut. t could not be explained as a deriv. from pre-Teut. d. But it is at least possible, on account of the great antiquity of the cognates, that they were borrowed from Lat. catapulta and remodelled.