V-Blocks are precision metalworking jigs typically used to hold round metal rods or pipes for performing drilling or milling operations.
They consist of a rectangular steel or cast iron block with a 120 degree channel rotated 45-degrees from the sides, forming a V-shaped channel in the top.
A small groove is cut in the bottom of the "V".
They often come with screw clamps to hold the work.
V-blocks are usually sold in pairs.