The difference is made up in the thickness of the Alcryn rubber. *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. Metric Uniseal® Pipe and Holesaw Size Table Nominal The table below indicates which Uniseals work well with metric sized pipe O.D's. Do not assume that the name of the pipe is the O.D. The sizes below will fit but check the Outside Diameter of your pipe. If you are using standard metric sized household pipes (popular in Hydroponics) the walls are thinner than pressure pipe. To check other metric sized pipes use the Pipe O.D. Some metric pipes have a near equivalence in size to the Imperial sized Uniseals so the 75mm metric pipe would fit into a Uniseal U275 for example. An example of this is is a 75mm metric pipe (O.D.) which has an internal diameter (bore) of around 67.8mm. Uniseals for Metric Pipe Sizes - Metric pipe sizes are denoted by the outside diameter (O.D.) of the pipe. U275 Uniseals can be directly replaced with U300 Uniseals. Some Uniseals fit into the same holesize and so are interchangeable e.g. Larger Uniseals have a tolerance of up to 2mm, however if your vessel is not pressurised you will get away with a little more. Uniseals will work perfectly on any pipe of the right O.D. The simplest thing to do is to measure accurately across the end of the pipe including the pipe wall thickness and match your Pipe O.D. to suit their Schedule 40 pipe standards. How do you determine what size of pipe you have and if it is suitable - Original Uniseals are ONLY made in Imperial sizes in the U.S.A. Makes sense when you think about it - higher pressure rating so a thicker wall in the pipe. An example of this is PVC/ABS pressure pipe which can have a thicker wall construction when the class number (pressure rating) increases. This can vary dependant upon pipe type, construction, and manufacturer.
6mm flexible PVC tube are denoted by their outside diameter (just to confuse things a little). a 3 inch pipe has an inside diameter of 3 inches. the Inside Diameter or bore of a pipe and how larger pipe size is denoted e.g. Water Flow Per Minute through associated pipework is a rough calculation and assumes gravity feed and low pressure systems. hole size of the Uniseal to create your seal. This is the most important size to match into the Pipe O.D. *3 Note 3 - Always measure the Outside Diameter (O.D.) of your pipe. Uniseals with the same hole size are interchangeable, handy if you have the smaller size and want to increase the flow.
*2 Note 2 - Uniseals U025 and U0312, Uniseals U050 and U075, Uniseals U275 and U300, Uniseals U400 and U400-SDR35 require the same sizes of holes. The actual Uniseal hole size for a 3/16" Uniseal required is 8 mm and can be created using a (sharp) drill bit. *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. Uniseal® Pipe and Holesaw Size Table Uniseal®