Understanding Speed Rail Dimensions

Jun 27, 2024




The video explains the sizing and measurement nuances of speed rail, a common material used in the film industry's grip and rigging departments. Speed rail, often referred to as inch and a quarter or inch and a half, does not correspond directly to those measurements because pipe is measured by internal diameter, originally intended for fluid transport. For instance, inch and a quarter pipe typically has an outside diameter of about inch and 5/8ths, and inch and a half pipe has an internal diameter close to inch and a half.


You might have wondered why speed rail that we commonly refer to as inch and a quarter or inch and a half doesn't actually measure to inch and a quarter or inch and a half. That's because pipe is measured from an internal diameter and not an external diameter. The reason for that is pipe is originally designed to carry fluid so it has more to do with the volumetric efficiency and capacity.

And then it's organized into schedules, once you have the size. Common use in our industry is schedule 40. If you measure the inside of an inch and a quarter pipe, you're gonna come to about 1.25 or inch and a quarter. And your OD, or your outside diameter, is gonna bring you pretty close to inch and 5 eighths. There are some tolerances there. With inch and a half, that's gonna be roughly inch and a half internal diameter.

And then mentioned 7-8ths outer diameter. You may have run into in the past some speed rail that didn't fit your fittings and have wondered why. The industry has some different tolerances. Again, they're more concerned with the inside than the outside. It's just been sort of an adaptation from our industry. Probably a carryover from the handrail industry when we started using Hollander fittings to build our rigs. Now that also brings us to talk about tube.

tube is measured outside to outside or an outside diameter. Now you can have square tube also, but you can't have square pipe. And most people will have on their truck some one inch square stock or three-quarter square stock. If you measure that, that's going to give you one inch outside to outside right on the nose there. And then there's also going to be a wall thickness. The standard in our industry for one inch square stock is going to be an eighth inch wall.

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