8 Series Single block works with 78-77 base only. Stainless Steel cheeks, Delrin(tm) sheave runs on Nomex(tm)/Teflon(tm) bearing for low-friction yet high strength operation. Spring mounted, on 1”-12 threaded stainless steel plug. Height = 4-5/8” (119mm) SWL: 2750 lbs. Works with 78-77 Base.