Pipes come in all sizes and are used for many different applications e.g. water, gas, electricity. Many are designed to work within their own systems and do not fit together with other systems.
Uniseals are made in Imperial sizes in the U.S.A. to fit their industrial pipe standard known as Schedule 40. This is a thick walled pipe we call Pressure Pipe as opposed to thin walled pipe used as standard in U.K. and European housing. There is not such a thing as a "Metric Uniseal". Many Uniseals will however work effectively with any pipe which has the correct Outside Diameter (O.D.).
When the application is not industrial e.g. fish ponds, Hydroponics, Aquaponics etc. a seal which withstands an industrial pressure of up to 65 P.S.I. is not required and the fit through a Uniseal does not have to be super tight as long as it remains waterproof at lower pressures. To give you something to guage pressure, mains pressure water is targeted at around 10 P.S.I. where it comes into our homes.
The table below indicates which Uniseals work well with metric sized pipe O.D's.
Metric Uniseal® Pipe and Holesaw Size Table
*1 Note 1 - Many websites show the required hole size for the 3/16 inch Uniseal as 10mm - it isn't and this would be realised by anybody who has fitted them. The actual Uniseal hole size for a 3/16" Uniseal required is 8 mm and can be created using a (sharp) drill bit.
*2 Note 2 - Although our full range is not shown here Uniseals U025 and U0312, Uniseals U050 and U075, Uniseals U275 and U300, Uniseals U400 and U400-SDR35 require the same sizes of holes. The difference is made up in the thickness of the Alcryn rubber. Uniseals with the same hole size are interchangeable, handy if you have the smaller size and want to increase the flow.
*3 Note 3 - Always measure accurately the Outside Diameter (O.D.) of your pipe.
Pipe sizes are often printed somewhere along the length of the pipe. To give you an example standard 40mm household pipe which is usually solvent welded (glued) is normally 43mm O.D. (and is a tough fit into a Uniseal U125) A better fit can be achieved in a U125 however with standard 40mm push fit pipe which actually has a smaller O.D.
Downloadable Metric Uniseal Hole Size Chart Image