The Gas Grenade shape is that of a cylinder. It does have a black release handle attached to the top/sides, but it still has the cylinder shape overall. The main body measures 4.0 inches tall and is 1.20 inches in diameter. This makes it a very narrow cylinder. Keep this in mind if you are cobbling your own gas grenade from found items. Too squat of a shape will throw off the look.
The grenade body has a deep Forest Green color. Very similar to a Brooklands Green used on Bentley Cars. The closest color we matched to it in the Pantone Color book was Pantone #7743.
The black paint used on the top of the grenade, and on release handle, was a basic Flat Black.
The leather holder is made up of multiple pieces of thin leather sewn together. The leather is painted green (closely matching Pantone 355 or 356) (For those wanting uber-accuracy, use a yellow base color beneath the green).
The leather holder has a long thin metal plate sandwiched inbetween the leather . This metal plate holds the holder in it's "L" shape.
This image was taken at the 2013 DragonCon Convention, taken from Rob Alsopp's archive Dredd Costume.
The belt loop on the back of the holder is riveted on the top and button snapped on the bottom. The rivets and buttons go through the metal plate and all the layers of leather.
The horizontal strap holding the Gas Grenade to the holder is made of two pieces of leather sewn togehter. They loop through the multiple layers of leather of the holder itself.
The Horizontal Strap uses a black .75 inch tri-glide clip and velcro to adjust the tension around the Gas Grenade.
Here is a mechanical blueprint of the grenade and release lever. Measurements were taken from a recast stunt grenade that was used in the movie (big thanks to the owner of the movie prop, Paul Wares, for offering the castings to the fans.)