PRODUCT MEASUREMENT TOOLS (GSR JERMAN)

T H R E A D  I D E N T I F I C AT I O N

To identify an unknown thread you need  to get two details: the pitch and the outer  diameter for a bolt thread or the inner diameter of a nut thread. The pitch is the gap between the flanks for metric threads or the number of pitches  per inch for inch threads.

 External thread

First you measure the diameter of the thread with a caliper. The digital caliper offers inch and metric units. The diameter will show you if it is a metric or an inch thread. You continue with the pitch gauge. Please test the single sheets until one of them  fits precisely into the thread.  Then you can read the pitch of the thread on the gauge which is printed onto  it. Now the thread slide is used which contains all details about the different  thread types. You can com- pare the measured values with the data  on the thread slide to find out the correct  thread type. All measuring tools are described on the following pages.

 

Internal thread

If it is relatively easy to determine the external  thread using the pitch gauge it is complicated to get the internal  thread size type. If you don’t want to destroy  the workpiece  and avoid major technical effort you can just roughly measure and try out. The procedure is as follows: Measure the core size of the thread with the outside leg of the caliper. This should  be the core hole size which has been  drilled before  the thread was cut. In our example  we measure an external diameter of 23 mm. The formula to determine core hole diameter is:

 dk = D – P(Core hole Ø = Nominal Ø – Pitch)

or: Nominal Ø = Core hole Ø + Pitch

 

 M E A S U R E M E N T

 Now you can check the core hole table  of the thread slide to find a suitable  core hole size. Hereby you have to regard  that  the core holes are mostly larger than  the guideline.  After calculating the example with the formula you get two possible  metric sizes M 24 × 1 or M

25 × 2 or one inch size G 5/8 × 14 pitch/inch. A decision  is made  by trying out the appropriate screws.



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