Blocks are basic building materials in Scrap Mechanic. They are distinguished by a blue dot in the inventory. There are a total of 87 different blocks available, including wedge counterparts and 3 exclusive to Challenge Mode.
Blocks are placed by left-clicking and removed by right-clicking. Hold down the mouse button to place or remove multiple blocks at once. This is restricted along one coordinate plane, indicated by the blue arrows in the center of the placement ghost. The placement/removal plane can be changed by pressing Q. The player can place or remove only 16 blocks in both directions from the initial block, making 256 the maximum amount of blocks that can be placed or removed at once.
According to the 2021 Q&A, the dimensions of a world tile is given as 64x64 meters. Since tiles measure 256x256 blocks, we can determine that a single block measures 25x25x25 cm.
Since the Physics & Wedges update, every block has a wedge counterpart. They have the same properties (weight, durability, etc.) as the normal blocks.