Machinery's Handbook, 31st Edition
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Microscope Objective Threads Table 1. Definitions, Formulas, Basic and Design Dimensions ANSI/ASME B1.11-1958 (R2016)
Table 1. (Continued) Definitions, Formulas, Basic and Design Dimensions
Symbol
Property
Formula
Dimension
Design Thread Form
h b - U = 0.566410 p
0.0157 0.0068 0.0046 0.00205 0.800 0.800 0.7941 0.7822 0.7822 0.7804 0.7644 0.7685 0.7626
Height of truncated Whitworth thread
k
Width of flat at crest Width of flat at root
0.243624 p 0.166667 p 0.073917 p
F c F r
Basic truncation of crest from basic Whitworth form
U
Basic and Design Sizes
Major diameter, nominal and basic Major diameter of internal thread Major diameter of external thread a Pitch (effective) diameter, basic
…
D
D
D n D s E n E s E K n K s K
D - 2U - G
D - h b D - h b
Pitch (effective) diameter of internal thread Pitch (effective) diameter of external thread b Minor diameter of internal thread Minor diameter of external thread a Allowance at pitch (effective) diameter a , b Minor diameter, basic
D - h
b - G
D - 2 h b D - 2 k
D - 2 h
b - G
G 0.0018 a An allowance equal to that on the pitch diameter is also provided on the major and minor diameters of the external thread for additional clearance and centralizing. b Allowance (minimum clearance) on pitch (effective) diameter is the same as the British RMS thread. All dimensions are in inches. Table 2. Limits of Size and Tolerances—0.800-36 AMO Thread ANSI/ASME B1.11-1958 (R2016) Element Major Diameter, D Pitch Diameter, E Minor Diameter, K Max. Min. Tol. Max. Min. Tol. Max. Min. Tol. External thread 0.7941 0.7911 0.0030 0.7804 0.7774 0.0030 0.7626 0.7552 a … Internal thread 0.8092 b 0.8000 … 0.7852 0.7822 0.0030 0.7715 0.7685 0.0030 … a Extreme minimum minor diameter produced by a new threading tool having a minimum flat of p ⁄ 12 = 0.0023 inch. This minimum diameter is not controlled by gages but by the form of the threading tool. b Extreme maximum major diameter produced by a new threading tool having a minimum flat of p ⁄ 20 = 0.0014 inch. This maximum diameter is not controlled by gages but by the form of the threading tool. Tolerances on the internal thread are applied in a plus direction from the basic and design size and tolerances on the external thread are applied in a minus direction from its design (maximum material) size. All dimensions are in inches. Lowenherz or Löwenherz Thread.— The Lowenherz thread is intended for the fine screws of instruments and is based on the metric system. It is a symmetrical thread, not a buttress thread. The Löwenherz thread has flats at the top and bottom the same as the US standard buttress form, but the angle is 53 degrees 8 minutes. The depth equals 0.75 × the pitch, and the width of the flats at the top and bottom is equal to 0.125 × the pitch. This screw thread is used for the fine threads of measuring instruments, optical apparatus, etc., especially in Germany.
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