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<strong>Cylindrical</strong> <strong>Roller</strong> <strong>Bearings</strong><br />
Fitting Practice<br />
The fitting practice given in the following tables conforms<br />
to industry <strong>and</strong> ABMA/ANSI st<strong>and</strong>ards, where<br />
applicable. The tables provide maximum <strong>and</strong> minimum<br />
sizes for bearing bore <strong>and</strong> O.D., shaft <strong>and</strong> housing<br />
bore, <strong>and</strong> the resultant effects of each type of fit.<br />
Dimensions are given in both inch <strong>and</strong> metric units with<br />
deviations in .0001 inch <strong>and</strong> micrometers.<br />
The looseness or tightness of a ring mounted on a shaft<br />
or in a housing bore depends on the conditions under<br />
which the bearing will operate <strong>and</strong> how it will be<br />
installed. The three most generally used fits are:<br />
PRESS, TAP AND PUSH.<br />
PRESS fit is used to fit a ring tightly to a rotating member<br />
(shaft or housing) to prevent creep or slippage that<br />
could result in damage to the shaft or housing bore.<br />
TAP fit usually accompanies PRESS fit, for fitting the<br />
opposite ring to the stationary member, if the bearing<br />
rings are separable.<br />
PUSH fit is used instead of TAP, for a stationary outer<br />
ring, if the bearing is non-separable.<br />
HEAVY PRESS fit (“A” style) is an <strong>NTN</strong>-Bower innovation<br />
for cylindrical roller bearings. It is used to prevent<br />
the outer ring from turning in the housing bore, where<br />
the bearing is operating under very heavy loads. The<br />
outer ring O.D. is made oversize to provide a heavy<br />
press fit in a st<strong>and</strong>ard (tap fit) size housing bore. The<br />
accompanying inner ring uses a PRESS fit on the shaft.<br />
The catalog fitting practice does not apply to bearings<br />
mounted on hollow shafts or in housings of materials<br />
softer than steel, such as as aluminum. Since these<br />
conditions Since these usually conditions require usually heavier require press heavier fits, the press <strong>NTN</strong><br />
Engineering fits, the <strong>NTN</strong> Department Engineering Department should be should consulted be consulted<br />
for<br />
for<br />
recommendation. recommendation.<br />
The chart on on the the opposite opposite page page summarizes summarizes the recommended<br />
fitting fitting practice practice for various for various installations installations <strong>and</strong><br />
the<br />
recommended<br />
<strong>and</strong> bearing bearing types, types, including including bearings bearings with inner with or inner outer or<br />
outer rings omitted. rings omitted.<br />
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