Eastonâ??s A/C ProComp arrow is available for compound target and field competition. ProComp is designed for top archers looking for the ultimate parallel shaft to boost scores at competitive and club-level compound events. The 4mm ProComp is an easy to tune shaft using accurate aluminum-carbon construction with reduced wind-drifting. Compatible with ACG and ACE components. Available in spine sizes 300(9.5 gpi.), 340 (8.9 gpi), 380 (8.3 gpi), 420 (7.8 gpi.), 470 7.3 gpi.), 520 (7.0 gpi.), and 570 (6.6 gpi.).