Yale Pulley blocks, hinged, with single steel sheave
Snatch Block Yarding Block Pulley 3" 1.5 Ton / 4" 3 Ton / 5" 4.5 Ton / 6" 6 Ton | eBay
How a Block and Tackle Works | HowStuffWorks
Block and Tackle Pulley System - Rope Hoist Pulley System - Heavy Duty Pulley System for Lifting Heavy Objects for Garage, Automotive, Warehouse Building: Amazon.com: Industrial & Scientific
4000LB Poly Rope Hoist Pulley Block and Tackle Rope with 7:1 Lifting Power, 2 To | eBay