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Insect and rodent screen comprising mesh cylinder, protected by perforated metal outer, with sleeve to slide over the end of a pipe and a worm drive clip to secure in place
End of Line Screen Clamp Fitting
Set of parts to provide insect screening for warning or overflow pipe, up to 23mm OD, comprising a tank connector, the screen holder and a dip pipe
Warning Pipe Kit
Insect screen in a moulded plastic body, supplied with moulded in BSP male threads and a lift-off inspection and cleaning cover
Inline Screen up to 2 inch
Insect and rodent screen fitted into a section of BS PVC pipe
Inline Screen 2½ inch and above
Insect and rodent screen in a stainless steel body, provided with BSP sockets at both ends
Inline Screen all stainless steel with BSP sockets
Insect and rodent screen in a stainless steel body, provided with bolted flanges at both ends
Inline Screen all stainless steel with flange
Cowl vent for small cisterns, comprising a holder for an insect screen, with a cowl over it to exclude dust and dirt, which pushes onto the end of a connector. The connector has an integral washer and cutting marks, to allow it to be reduced in length by 25mm or 50mm, and is supplied with two EPDM washers and a ¾ inch BSP nut
Cowl Vent ¾ inch BSP
Grey PVC vent with insect screen. 4 inch BSP threaded shaft, fitted with two PVC nuts, one with a conformable foam washer. Grey PVC cowl over screen.
Cowl Vent 4 inch BSP
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Pipe Sizes


Although Britain adopted the metric system in the 1970s, there were many areas where imperial measurements were too widely used for it to be possible for the change to be complete. As pipes can last for decades, the sizing of pipework is one such area. There are, therefore, still two different systems in use today; the metric and the imperial systems.

Metric - Copper Pipe and Waste Pipe

The size of a metric pipe is given in millimeters and is measured across the outside diameter of the pipe. This system has been universally adopted on copper plumbing since 1971 and imperial copper pipe will now only be found in older installations. Some plastic and stainless steel pipe for industrial applications is also measured this way.

Some suppliers also use metric measure to describe steel and BS 3505 plastic pipe. For example, 4 inch plastic drain pipe may be sold as 110mm or 115mm.

Plastic waste pipes are also measured in millimeters in sizes from 21mm to 50mm, but the actual size may vary between manufacturers. We cannot guarantee that our screens can be used with waste pipe (normally white) unless the product data sheet specifically describes the screen as suitable for use with it.

Imperial Measure - Steel and BS 3505 Plastic Pipe

The size of an imperial measure pipe is given in inches (1 inch = 25.4mm) and fractions of inches and is measured across the inside diameter of the pipe. The outside diameter will, therefore, be this plus the wall thickness and will be larger than the size used to describe the pipe. Imperial measure is used for British Standard 3505 uPVC pipes (normally grey) and for steel pipes.

The table below shows the nominal external diameter of pipe sizes from ½ inch to 8 inches bore for steel pipe. PVC pipe will be similar, but the wall thickness varies according to the pressure rating.

Table of British Standard Pipe sizes
Pipe bore Pipe OD Imperial Pipe OD Metric
½ inch
¾ inch
1 1/16"
1 inch
1 3/8"
1¼ inch
1 11/16"
1½ inch
1 29/32"
2 inch
2 3/8"
2½ inch
2 7/8"
3 inch
4 inch
4 17/32"
5 inch
6 inch
7 inch
7 5/8"
8 inch
8 5/8"


For details of thread sizes, up to 4 inches, see the British Standard Pipe Thread page.