Single Ball Bearing 38mm Block This is an upgraded version of the classic Laser mainsheet block used in the middle of the Laser boom to guide the mainsheet back from the boom to the deck. This block is Laser class legal. Manufactured from nylon and features a ball-bearing sheave for reduced friction.Originally designed for the Laser dinghy mainsheet system this classic block has also become the block of choice for many other dinghy mainsheet systems.