These Sonar mast blocks made by JCD from rugged HDPE. They are easy to move and even float. Width is 2-7/8 in. All have a high side with a finger hold. Alternating these leaves the high side exposed for easy access. They have a nice big 1.25 in hole in the middle for less weight. The mast block consist of (4) 1/2 in, (2) 1/4 in, and (2) 1/8 in blocks for a total thickness of 2-3/4 in.