2 Bolts Low profile Allen socket head M16x35mm and 4 nuts M16.
Vice, welding machine, angle grinder, file.
Place/adjust two pairs of nuts at the vice so as the bolts can screw/unscrew correct and freely.
Tack welds the sides of nuts using the combination:
single sides 1-3-5 at first and then the even sides 2-4-6.