Standard bolt taper 1⁄16 inch per foot.
Length of bolts from head to end of thread equals a.
Diameter of bolt under the head as follows:—
| 3⁄64 | inch | larger at b | for 9 inch and under | |||||
| 1⁄16 | „ | „ | over | 9 | inch | to | 12 | inch |
| 3⁄32 | „ | „ | „ | 12 | „ | to | 18 | „ |
| 1⁄8 | „ | „ | „ | 18 | „ | to | 24 | „ |
| 5⁄32 | „ | „ | „ | 24 | „ | to | 30 | „ |
| 3⁄16 | „ | „ | „ | 30 | „ | to | 36 | „ |
Fig. 1402.
It is obvious that a plug or collar gauge simply determines what is the largest dimension of the work, and that although it will demonstrate that a piece of work is not true or round yet it will not measure the amount of the error. The work may be oval or elliptical, or of any other form, and yet fit the gauge so far as the fit can be determined by the sense of feeling. Or suppose there is a flat place upon the work, then except in so far as the bearing marks made upon the work by moving it within the gauge may indicate, there is no means of knowing whether the work is true or not. Furthermore, in the case of lathe work held between the lathe centres it is necessary to remove the work from the lathe before the collar gauge can be applied, and to obviate these difficulties we have the caliper gauge shown in [Fig. 1402]. The caliper end is here shown to be for 3⁄4 inch, and the plug end for 13⁄16 inch. If the two ends were for the same diameter one gauge only would be used for measuring external and internal work of the same diameter, but in this case the male cannot be tested with the female gauge; whereas if the two ends are for different diameters the end of one gauge may be tested with that of another, and their correctness tested, but the workman will require two gauges to measure an external and internal piece of the same diameter.
