What size T-slot nutsbolts do I want to get for the 20x20 Aluminum

What size T-slot nutsbolts do I want to get for the 20x20 Aluminum t slot 2020 TSLOTS 20-2020 20mm x 20mm 6mm t slot tonneau cover What is the best way to build aluminum extrusion, with T or V slot?In Part Studio assembly?

t slot tonneau cover High strength ZYLtech 2020 aluminum extrusions are made of 6063-T5 aluminum alloy The T slot features smooth rounded edges and is compatible with ZYLtech

tower quest slot 20-2020 is a 20mm x 20mm metric 20 series square T-slot profile with four open T-slots, one on each 20mm face The profile is smooth, which makes it resistant Black T slot European Standard Linear Rail 4040 2020 Aluminum Profile Extrusion for DIY 3D Printer Workbench $