A screw spike, rail screw (or lag bolt) is a large (~6 in or 152 mm length, slightly under 1 in or 25 mm) metal screw used to fix a tie plate or fasten rail. Screw spikes are fixed into a hole bored in the sleeper. The screw spike has a higher cost to manufacture than the rail spike but has the advantage of greater fixing power; approximately twice that of a rail spike, and can be used in combination with spring washers.
