You are Here: Home > Helpful Resources > Decimal Equivalents of Fraction, Wire, and Letter Sizes

for Mil Spec, ANSI or ACME part number

Standard Metric Bushings Technical Information

No-Counterbore Bushings are Standard with ACME

Acme is committed to the concept of manufacturing our bushings without a counterbore. No-Counterbore bushings are more difficult and costly to produce, because close tolerances are required the full length of the bushing. We believe this produces a better, longer lasting and more versatile bushing. Counterbored bushings will be supplied only upon special request.

Plain Press Fit Bushings -Type PM

Head Press Fit Bushings - Type HM

Slip-Fixed Renewable Bushings - Type SFM

Plain Liners - Type PM

Head Liners - Type HM

  • Similar to Plain Liners but with a head or shoulder
  • Use with Slip-Fixed Renewable bushings whenever excessive pounding or force will occur during operation
  • Head prevents liner from being pushed through jig plate
  • Flush mount by counterboring top of hole in jig plate
  • Length is measured overall
  • Head Liners are the same as Head Press Fit Bushings
  • Bushing Installation

    Production accuracy requires extra care when preparing mounting holes and installing bushings/liners. The following factors should be considered: interference fits, alignment, chip clearance, and how close the bushing is to the workpiece.

    Because of the many variables, no definite rules can substitute for the skill and judgment of the experienced toolmaker.

    Interference Fits

    Interference holds press fit bushings in the jig plate. Too much interference may cause a number of problems: (1) jig plate distortion; (2) bellmouthing (bushing/liner walls bow inward); (3) tool seizure, or (4) trouble with slip-fixed renewable fitting into the liner. Too little interference may allow slippage, thus causing inaccurately drilled holes.

    Mounting Hole Preparation

    It is recommended that all mounting holes be jig bored or sized with a reamer to assure roundness. Bushings tend to assume the shape of the hole they are pressed into. See chart below for recommended size.

    The recommended installation hole size should be in accordance with metric tolerance class H7.

    Nominal O.D. Recommended Hole Size
    4 to 6 Nominal +0/+.012
    7 to 10 Nominal +0/+.015
    12 to 18 Nominal +0/+.018
    22 to 30 Nominal +0/+.021
    35 to 48 Nominal +0/+.025
    55 to 78 Nominal +0/+.030
    85 to 115 Nominal +0/+.035
    125     Nominal +0/+.040

    Press Fit Bushing Installation

    First, lubricate the inside diameter of the mounting hole and the outside diameter of the bushing/liner.

    Second, use an arbor press to press the bushing/liner into place. If an arbor press is not available, draw the bushing/liner into place by tightening two steel plates connected by a nut and bolt. Maintain centerline perpendicularity.

    Bushing Features

    Inside Diameter Tolerances

    The minimum and maximum allowance for the Inside Diameter of standard bushings is in accordance with metric tolerance class G6. Special bushings will be supplied with the tolerances shown, unless specified otherwise.

    Standard Drill Bushings:

    I.D. Range (Drill Size) Standard I.D. Tolerance (add to nominal I.D.)
    0.35 to 3.00 +.002 to +.008
    3.01 to 6.00 +.004 to +.012
    6.01 to 10.00 +.005 to +.014
    10.01 to 18.00 +.006 to +.017
    18.01 to 30.00 +.007 to +.020
    30.01 to 50.00 +.009 to +.025
    50.01 to 80.00 +.010 to +.029
    80.01 to 105.00 +.012 to +.034

    Reamer Bushings:

    I.D. Range (Drill Size) Standard I.D. Tolerance (add to nominal I.D.)
    1.00 to 3.00 +.006 to +.012
    3.01 to 6.00 +.010 to +.018
    6.01 to 10.00 +.013 to +.022
    10.01 to 18.00 +.016 to +.027
    18.01 to 30.00 +.020 to +.033

    Reamer Bushings are considered specials and are priced accordingly. When ordering specify the letters “RM” after the I.D.

    Outside Diameter Tolerances

    The minimum and maximum metric tolerance for the Outside Diameter of standard press fit bushings is class s6 and class h5 for slip-fixed renewable bushings.

    Ordering Information

    To order metric bushings please provide the quantity required, ANSI Symbol, and inside diameter. The order for 26 pieces of a 38 mm I.D., by 55 mm O.D., by 30 mm long, Type PM bushing should appear as follows:

    Qty. Type O.D. (in mm) Length (in mm) I.D. (in mm)
    26 pcs. PM —     55 —     30 —     38.00

    ISO 9001

    Aerospace Industries