Abstract: An extensible boom, which comprises a first part which is pivotally anchored to a rotatable pedestal so that the boom may be raised or lowered. A second part of smaller lateral dimension is adapted to slide within the first part. The outer end of the second part carries a crown, with at least two crown sheaves. On the inner end of the second part there are two pulleys having transverse vertical pins about which they rotate. On the outer end of the first part there is a third pulley having a shaft substantially horizontal. A conventional cable drum is supported on the pedestal with conventional drive means. The cable spools from the drum over one of the crown shafts down to a travelling block and hook and is arranged over said pulleys in a manner such that when there is a weight hanging on the hook, there will be a force tending to extrude the second part out of the first part, unless it is held back by a tension member.

Abstract: A travelling block system that can be changed quickly from a four support line system to a two support line system, which comprises a travelling block having two sheaves, and a single sheave block with hook, attached to the crown of a boom. The two sheave travelling blocks comprise a frame with two parallel spaced plates serving as inner sheave plates, two sheaves on the outside of the inner sheave plates, and two outer sheave plates. The sheave plates are firmly bolted to the frame, and appropriate sheave pins are supplied through each pair of outer and inner sheave plates. Two guard strips are provided which are removably attached around the periphery of the outer and inner sheave plates so as to completely contain the cable around the sheave on sides and bottom of the sheaves.

Abstract: An improved hoisting hook or becket including an upper body member having an eye in the upper portion for receiving a cable, hook or the like for lifting the becket and any load attached to it, the body having spaced apart openings near the bottom edge, a lower U-shaped shank member having ends which are in a common plane and having openings near each of the ends, the openings in the shank and body being substantially equidistant and a pair of links each having parallel side plates and parallel horizontal upper and lower pins, the lower pins of each link being received in the openings in the shank and the upper pin of one of the hooks being received in the first opening in the body so that the shank is pivotal relative to the body, the second opening in the body having open communication through the top of the body member and providing means so that the upper pin of the second link can be slidably moved into and out of the second opening, the dimensions of the body, shank, hook and links being arranged such t