PLAIN GAUGES, LIMITS AND FITS
Plain gauges generally fall into two types:– plugs for internal holes,
and rings or gaps, sometimes referred to as ‘snap’ or caliper
gauges for shafts.
The tolerance and position of a hole or shaft is described by a letter and
a number. A capital letter denotes a hole and a small letter a shaft. The
letter describes the position of the component tolerance relative to the nominal
size, and the number denotes the magnitude of the tolerance. Thus H8 for a
hole or h8 for a shaft.
The letters range from A or a to Z or z and are divided into three main classes:–
clearance; transition and interference. A fit between hole and shaft is described
as e.g. H8–f8. The numbers range from 1 to 16.
It is possible to combine any shaft with any hole but it is recommended that
the ‘unilateral hole system’ be adopted with ‘H’ being
the standard hole. Conversely a ‘unilateral shaft system’ with
‘h’ as the standard shaft may also be used.
The magnitude of the tolerance remains the same regardless of position, e.g.
the hole of say K8 has the same tolerance as an H8. Only the position is changed
relative to the basic size.
A more detailed explanation of the system is given in
BS 4500:Section 1.1: 1990 and BS 4500: Section
1.2:1990 for metric limits and fits and BS
1916 Parts 1, 2 & 3 for inch sizes. Plain limit gauges are manufactured
to BS 969:1982, which specifies tolerancing
of the gauges themselves.
| Plain Plug Gauges - Steel (reversible design steel) | ||||
| Size | Double Ended | Single Ended | Member only | |
| mm | inch | |||
| 0.25-0.40 |
0.010-0.015 |
HO31 | HO31S | HO31M |
0.40-0.75 |
0.015-0.030 |
HO32 | HO32S | HO32M |
0.75-6.00 |
0.030-0.250 |
HO33 | HO33S | HO33M |
6.00-11.00 |
0.250-0.4375 |
HO34 | HO34S | HO34M |
11.00-12.50 |
0.4375-0.500 |
HO35 | HO35S | HO35M |
12.50-16.00 |
0.500-0.625 |
HO36 | HO36S | HO36M |
16.00-19.00 |
0.625-0.750 |
HO37 | HO37S | HO37M |
| Plain Plug Gauges - Steel (Taper lock design - steel) | ||||
| Size | Double Ended | Single Ended | Member only | |
| mm | inch | |||
| 3.00-9.50 | 0.125-0.375 | HO11 | HO11S | HO11M |
| 9.50-12.50 | 0.375-0.500 | HO12 | HO12S | HO12M |
| 12.50-17.50 | 0.500-0.687 | HO13 | HO13S | HO13M |
| 17.50-22.00 | 0.687-0.875 | HO14 | HO14S | HO14M |
| 22.00-25.50 | 0.875-1.000 | HO15 | HO15S | HO15M |
| 25.50-28.50 | 1.000-1.125 | HO16 | HO16S | HO16M |
| 28.50-32.00 | 1.125-1.250 | HO17 | HO17S | HO17M |
| 32.00-38.00 | 1.250-1.500 | HO18 | HO18S | HO18M |
| 38.00-44.50 | 1.500-1.750 | HO19 | HO19S | HO19M |
| 44.50-51.00 | 1.750-2.000 | HO110 | HO110S | HO110M |
| 51.00-57.00 | 2.000-2.250 | HO111 | HO111S | HO111M |
| 57.00-65.00 | 2.250-2.500 | HO112 | HO112S | HO112M |
| Plain Plug Gauges - Steel (TRI lock Design - steel) | ||||
| Size | Double Ended | Single Ended go | Member End n/go | |
| mm | inch | |||
| 19.00-25.00 | 0.750-1.000 | HO21 | HO21G | HO21N |
| 25.00-32.00 | 1.000-1.250 | HO22 | HO22G | HO22N |
| 32.00-38.00 | 1.250-1.500 | HO23 | HO23G | HO23N |
| 38.00-50.00 | 1.500-2.000 | HO24 | HO24G | HO24N |
| 50.00-63.00 | 2.000-2.500 | HO25 | HO25G | HO25N |
| 63.00-75.00 | 2.500-3.000 | HO26 | HO26G | HO26N |
| 75.00-90.00 | 3.000-3.500 | HO27 | HO27G | HO27N |
| 90.00-100.00 | 3.500-4.000 | HO28 | HO28G | HO28N |
| 100.00-115.00 | 4.000-4.500 | HO29 | HO29G | HO29N |
| 115.00-125.00 | 4.500-5.000 | HO210 | HO210G | HO210N |
| 125.00-140.00 | 5.000-5.500 | HO211 | HO211G | HO211N |
| 140.00-150.00 | 5.500-6.000 | HO212 | HO212G | HO212N |
| 150.00-180.00 | 6.000-7.000 | - | HO213G | HO213N |
| 180.00-200.00 | 7.000-8.000 | - | HO214G | HO214N |
| 200.00-230.00 | 8.000-9.000 | - | HO215G | HO215N |
| 230.00-250.00 | 9.000-10.000 | - | HO216G | HO216N |
