Series 8 blocks have stainless steel cheeks and Series 9 blocks have black aluminum cheeks. They offer the high strength and low friction needed to bridge the gap between medium-sized racing or cruising yachts and larger offshore designs. These are the blocks to have when you sail to remote locations where trouble-free performance is paramount. They feature bolted construction, so they can be easily disassembled for maintenance or parts replacement.Line-only models come with Delrin sheaves and a friction-reducing, Teflon impregnated bushing. UC models feature Universal Circuit Sheaves that are among the smoothest spinning sheaves available. They incorporate an aluminum alloy sheave for high-tech lines or wire, slippery Nomex/Teflon bushings and dual races of Delrin 107 ball bearings. They are precision engineered to withstand heavy static loads on the Nomex bearing, yet still run free on the ball bearings when lightly loaded 8 series stainless blocks come with black Delrin sheaves for line only, or hardcoat aluminum UC sheaves Black anodized aluminum Series 9 blocks come with white Delrin sheaves or UC sheaves Easy spinning Nomex/Teflon bushing system with traces of Teflon is immune to load-induced distortion, point loading or maintenance associated with roller bearings Investment cast, three-way stainless head, forged "D" shackles Sheave diameter: 2-3/8" Pin diameter: 5/16" SWL: 2,750 lbs.