Here is a link to the 25mm long set screw/grub screws I ordered for mine, works well (they have other lengths as well).I have Lishen 280Ah cells likely the exact same as 272Ah ones that are supposed to do 285Ah. they have M6 set screws that use a 3mm hex key to tighten into place, they came with bus bars and serrated flange nuts also 16mm x M6. I am almost positive none are M4 as M6 is only like 1/4 inch diameter anyway. they are small. the set screws are also referred to as grub screws. mine set screws were a little short for thicker lugs so I ordered some longer stainless steel 25mm and 30mm M6 grub screws.
Stainless Steel Flat-Tip Set Screw - McMaster-Carr