Railway Lag Screw

A railway lag screw (also known as a screw spike, sleeper screw, or rail screw) is a heavy-duty metal fastener used to secure railroad tie plates or rails directly to wooden or concrete sleepers. Unlike traditional rail spikes, which are hammered in, lag screws are screwed into pre-drilled holes, providing approximately twice the fixing power and greater resistance to loosening from vibrations. 

Key Features and Types

1. Design: Typically features a thick, sturdy shaft with coarse, deep threading designed to bite into wood or engage with plastic dowels in concrete.

2. Head Types: Usually has a hexagonal or square head, allowing it to be tightened with a wrench or socket driver to apply high torque.

3. Durability: Often made from high-carbon steel and treated with coatings like hot-dip galvanization, zinc, or black oxide to resist corrosion in harsh outdoor environments.

4. Dimensions: Common sizes range from 5.5 to 10 inches in length, with diameters typically just under 1 inch (approx. 24mm). 

Rail Spike vs. Railway Lag Screw

1. Feature         Rail Spike (Dog Spike)     Railway Lag Screw

2. Installation Hammered/Driven             Screwed (requires pilot hole)

3. Fixing Power Standard                                   ~2x greater than spikes

4. Maintenance Higher (loosens over time)    Lower (vibration resistant)

5. Cost               Less expensive               More expensive to manufacture

Installation Process

To properly install a railway lag screw into a wooden tie, a pilot hole must be drilled first. This hole should be slightly smaller than the screw's diameter to allow the threads to bite into the wood without splitting it. The screw is then driven in using a wrench, socket, or specialized pneumatic device.