Various clamps made for the attach angles. Holding the 032 attach angles in place for drilling requires clamps with special clearance for the attach angle flanges.
The clamps are habor freight. They are probably cast iron. I use a dremel to cut out areas required to make screw threads.
The white material is copolymer rod from amazon. Usually, about $8 for 1 foot lengths of different diameters.
The acme screw has a piece of copolymer rod that has been bored out enough for the foot of the clamp to fit inside. I then use epoxy to hold the copolymer material to the foot.