stud sizes for ATR header install on GN1R Aluminium heads?

[2GNS4ME]

I was told its better to use studs when installing atr headers on aluminum heads. Anyone know the proper sizes?

Thanks
2gns4me

 

[2GNS4ME]

ttt

 

[turbofabricator]

3/8-16 is the thread size. Length will depend on header flange thickness.