Harken 38mm Double Big Bullet Block [127] Marine Safety | Waterproof Bags & Cases Covering the mounting holes that

Covering the mounting holes that would otherwise be visible

Hydraulic tubing and hardware

Other brands just link together their single blocks

Buoyant/floats

automatic back-flow prevention is incorporated into the design

Harken 38mm Double Big Bullet Block [127] Marine Safety | Waterproof Bags & Cases Covering the mounting holes that38mm Double Big Bullet Block Low friction Bullet blocks lead control lines aft. They are compact and lightweight, with fast trim and release under high or low loads. A range of styles lets these blocks adapt to almost all control line applications. Features: Sheave: 38mm (1 1 2") Maximum Line: 10mm (3 8") Maximum Working Load: 272kg (600lb)