Tyrol provide a pair of ARP bolts with the kit for 2 of the collars. The rest of the bolts just use new standard GTI ones. And do replace them as stretch bolts must not be reused. If you really must reuse them (bolts are expensive these days, I get it), just torque the 18mm ones to 100nm and the 16mm ones to 70nm. Do not redo the 90 degree angle!