This is for the V1 only
GiGDigit - Square Nut with Set Screw - MP Select Mini V1 - MP Mini Delta - Malyan M100 (Qty 2)
The “set screw” or “grub screw” that holds the heatbreak and Bowden tube connectors is M3-0.5 x 5mm (6mm will probably work) and takes a 1.5mm Allen wrench or 1/16“ Allen wrench.
Amazon.com - Set Screw, M3 x 5mm (10)
HomeDepot.com - M3-0.5 x 5 mm Alloy Metric Socket Set Screw (2-Pack)
The square nut is M3-0.5 It is 5.45mm square and 2.45mm thick.
Amazon.com - Honbay 100pcs 304 Stainless Steel M3 Square Nuts
Amazon.com - DD-life 100pcs 304 Stainless Steel Square Nuts M3