Page 278 - Aeronautical Engineer Data Book

224 Aeronautical Engineer’s Data Book
Table 12.3 Classes of fit (imperial)
1. Loose running fit: Class RC8 and RC9. These are
used for loose ‘commercial-grade’ components where
a significant clearance is necessary.
2. Free running fit: Class RC7. Used for loose bearings
with large temperature variations.
3. Medium running fit: Class RC6 and RC5. Used for
bearings with high running speeds.
4. Close running fit: Class RC4. Used for medium-speed
journal bearings.
5. Precision running fit: Class RC3. Used for precision
and slow-speed journal bearings.
6. Sliding fit: Class RC2. A locational fit in which close-
fitting components slide together.
7. Close sliding fit: Class RC1. An accurate locational fit
in which close-fitting components slide together.
8. Light drive fit: Class FN1. A light push fit for long or
slender components.
9. Medium drive fit: Class FN2. A light shrink-fit
suitable for cast-iron components.
10. Heavy drive fit: Class FN3. A common shrink-fit for
steel sections.
11. Force fit: Class FN4 and FN5. Only suitable for high-
strength components.

Table 12.4 Force and shrink fits (imperial)
Nominal size Class
range, in
FN1 FN2 FN3 FN4 FN5

0.04–0.12 0.05 0.2 0.3 0.5
0.5 0.85 0.95 1.3
0.12–0.24 0.1 0.2 0.95 1.3
0.6 1.0 1.2 1.7
0.24–0.40 0.1 0.4 0.6 0.5
0.75 1.4 1.6 2.0
0.40–0.56 0.1 0.5 0.7 0.6
0.8 1.6 1.8 2.3
0.56–0.71 0.2 0.5 0.7 0.8
0.9 1.6 1.8 2.5
0.71–0.95 0.2 0.6 0.8 1.0
1.1 1.9 2.1 3.0
0.95–1.19 0.3 0.6 0.8 1.0 1.3
1.2 1.9 2.1 2.3 3.3
1.19–1.58 0.3 0.8 1.0 1.5 1.4
1.3 2.4 2.6 3.1 4.0
1.58–1.97 0.4 0.8 1.2 1.8 2.4
1.4 2.4 2.8 3.4 5.0
1.97–2.56 0.6 0.8 1.3 2.3 3.2
1.8 2.7 3.2 4.2 6.2
2.56–3.15 0.7 1.0 1.8 2.8 4.2
1.9 2.9 3.7 4.7 7.2
Limits in ‘mils’ (0.001 in).