ARP Head Stud Kit for 83-89 Porsche 944 2.5L SOHC / DOHC Water Cooled Engine. Socket Size(s) – 5/8 12pt, 5mm Allen. CP Cometic ACL Ferrea and ARP Kits. Custom Made Package Deals. Head and Main Studs. Your address must be confirmed. Buyers who pay with unconfirmed addresses will not be accepted. We always look to satisfy our customers in whatever needs they may have.