Hose and Coupling Knowledge Base

This topic is about hose sizes.

Toyox’s TOYORON Hose line ranges from 4 millimeters in diameter to 75 millimeters, in 16 sizes. The sizes do not increase uniformly, however, and it is difficult to figure out how the sizes were determined. Are hose sizes determined by law?

Hose lengths come in a variety of units, including meters, feet, inches and native Japanese lengths. Most Japanese catalogs list lengths in meters.

Today, hoses are usually connected using a specialized hose coupling that the hose fits into, but previously, hoses were directly connected to pipes. Vinyl chloride and other pipes are sized in inches. Here are some basic approximate conversions:
1 inch = 25 mm
3/4 inch = 19 mm
5/8 inch = 15 mm
1/2 inch = 12.7 mm

Because the outer diameter is used as the size for pipes, hoses, which are inserted into pipes, are sized by their inner diameter. Most Japanese catalogs indicate the inner diameter of hoses in millimeters, and therefore the sizes may seem haphazard.

In Japan, hoses are also measured in bu. The bu is part of the traditional Japanese measuring system, and at one-hundredth of a shaku is about 3 millimeters. Coincidentally, this is very close to an eighth of an inch. One inch is 25.5 millimeters, and one-eighth of an inch is 3.175 millimiters. It should be noted that the bu used for steel pipe measurement is slightly different.