The Allen Vang Block with Key and the Allen Fiddle Block with V-Jam Cleat are designed for simple purchase systems, such as vangs. The former is the block of choice among Laser sailors for upper vang replacement, while the latter is the choice for lower vang replacement. Allen Plain Bearing Blocks have been adopted by the Laser class as the block to use for the mainsheet system. 

Allen Snatch Blocks feature dynamic bearing technology with an easy-to-use mechanism for opening and closing the cheeks. Allen also makes Stanchion Mounted Blocks for leading lines from the foredeck aft to the cockpit. They're perfect for furling leads, and they can be found under "Sailboat Hardware & Rigging - Headsail Handling - Furling Blocks & Leads."
Allen Vang Block with Key - 25mm
Item # 210563
Allen Plain Bearing Blocks - 29 & 38mm
Item # WAPBB2938
Starting from $13.28
Allen Snatch Blocks - 30 & 40mm
Item # WASB3040
Starting from $39.90