It is a short straight length of radiator-grade rubber hose used to join two pipe stubs or two lengths of hose together. Typical uses are repairing a split section without replacing a whole moulded hose, extending a coolant run, adapting between hard pipes on a custom installation, or joining hard pipework in agricultural and industrial systems where a little flexibility absorbs vibration.

Internal diameters from 5mm right up to 102mm - 25 sizes - in lengths of 50mm, 75mm and 100mm for short joins, and 250mm, 500mm and 750mm where you need to bridge a longer gap. Order by internal diameter to match the outside diameter of the pipe stubs you are joining. If both stubs are different sizes you need a reducer rather than a straight coupler.

It is EPDM rubber built to SAE J20 R3 with an operating range of -30C to +120C, and it is glycol rated, so it is suitable for standard antifreeze mixes. That covers the great majority of automotive, marine, agricultural and industrial cooling systems. For higher temperatures or for fuel and oil, EPDM is the wrong material - move to our silicone or fluorosilicone ranges.

As a rule of thumb, aim for at least 25mm of pipe engaged at each end on smaller bores and proportionally more on the larger sizes, with the clip sitting squarely over the supported section rather than near the open end. A 50mm coupler joining two stubs gives you roughly 25mm each side, which is the minimum - if you have room, a 75mm or 100mm coupler makes a more secure joint.

Rubber is the like-for-like choice for a standard cooling system, it is cheaper, and it matches the feel of the original hoses. Silicone is the upgrade: much higher temperature capability, it will not perish or harden with age, and it is available in colours. For a repair on a daily driver or a piece of plant, rubber is perfectly sensible. For a performance build or anywhere running hot, go silicone.

It is an assortment of radiator hose sections in a variety of diameters and lengths, made from the same EPDM material to the same SAE J20 R3 specification. It is a genuinely useful thing to have on a workshop shelf or in a van - when you need a short join at short notice, the chances are the box has something close. It is priced well below buying the equivalent lengths individually.