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#1
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markings on Screw Pitch Gauge?
I've got an old screw pitch gauge that I inherited. There's no mfr's
name marked on it, just "Number 137". the individual leaves are marked with two numbers each, but these numbers are not reciprocals. The first number is always a small integer which I presume is threads-per-inch. the second number is always a decimal. All the leaves are of equal thickness, so they are not thickness calibrations as in a feeler gauge. Any idea what the second set of numbers are? |
#2
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Probably metric (in millimeters pitch)
Don "Alan Horowitz" wrote in message om... I've got an old screw pitch gauge that I inherited. There's no mfr's name marked on it, just "Number 137". the individual leaves are marked with two numbers each, but these numbers are not reciprocals. The first number is always a small integer which I presume is threads-per-inch. the second number is always a decimal. All the leaves are of equal thickness, so they are not thickness calibrations as in a feeler gauge. Any idea what the second set of numbers are? |
#3
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#4
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"John Manders" wrote in message ... "Alan Horowitz" wrote in message om... I've got an old screw pitch gauge that I inherited. There's no mfr's name marked on it, just "Number 137". the individual leaves are marked with two numbers each, but these numbers are not reciprocals. The first number is always a small integer which I presume is threads-per-inch. the second number is always a decimal. All the leaves are of equal thickness, so they are not thickness calibrations as in a feeler gauge. Any idea what the second set of numbers are? Depends upon whether it's metric or imperial. The most likely is that the first is TPI, as you say. The second is probably the bolt diameter in a thread series. The most likely is BSW. John The second set of numbers, decimals, is the double depth of the thread pitch .. Harold |
#5
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Alan, while awaiting the answer from those more knowledgeable, see if you
can borrow a Machinery's Handbook. Most machinists and mechanical draftsmen will have a copy. It will explain more than you want to know about threads. And, the American Standards Association (ASA) sets the standard on screw threads and a whole bunch of other things as well. Alan Horowitz wrote: I've got an old screw pitch gauge that I inherited. There's no mfr's name marked on it, just "Number 137". the individual leaves are marked with two numbers each, but these numbers are not reciprocals. The first number is always a small integer which I presume is threads-per-inch. the second number is always a decimal. Any idea what the second set of numbers are? pairs of numbers are ~~~~~~~~~~~~~~~~~~~~ 60 - 0.021 48 - 0.026 40 - 0.032 32 - 0.040 30 - 0.043 28 - 0.046 26 - 0.049 25 - 0.051 24 - 0.063 22 - 0.058 20 - 0.064 19 - 0.067 16 - 0.080 14 - 0.091 13 - 0.098 12 - 0.107 11 - 0.115 10 - 0.126 9 - 0.142 8 - 0.160 7 - 0.183 6 - 0.215 5 - 0.259 4-1/2 - 0.284 (sic) 4 - 0.320 looking at the leaves, "depth of thread" in inches seems the most plausible to me. This item would date back to the 50's, I don't believe there was too much metric action in American machine shops at that time. I'd try _measuring_ the depths with a micrometer, but I don't know where to measure to/from. How is thread depth defined? And by the way, who sets the standards on how these things are measured? |
#6
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"Jim Pugh" wrote in message ... Alan, while awaiting the answer from those more knowledgeable, see if you can borrow a Machinery's Handbook. Most machinists and mechanical draftsmen will have a copy. It will explain more than you want to know about threads. And, the American Standards Association (ASA) sets the standard on screw threads and a whole bunch of other things as well. Alan Horowitz wrote: I've got an old screw pitch gauge that I inherited. There's no mfr's name marked on it, just "Number 137". the individual leaves are marked with two numbers each, but these numbers are not reciprocals. The first number is always a small integer which I presume is threads-per-inch. the second number is always a decimal. Any idea what the second set of numbers are? pairs of numbers are ~~~~~~~~~~~~~~~~~~~~ treat the first number as TPI I have added witworth form thread depth in inches..... doubleing it gives the second number. 60 - 0.021 0.0160009 48 - 0.026 0.013340 40 - 0.032 0.016008 32 - 0.040 0.020010 30 - 0.043 28 - 0.046 0.022869 26 - 0.049 0.024628 25 - 0.05 24 - 0.063 0.026681 22 - 0.058 0.029106 20 - 0.064 0.032016 19 - 0.067 0.033702 16 - 0.080 0.040020 14 - 0.091 0.045738 13 - 0.098 12 - 0.107 0.053360 11 - 0.115 0.058212 10 - 0.126 0.064033 9 - 0.142 0.071147 8 - 0.160 0.080041 7 - 0.183 0.091475 6 - 0.215 0.106721 5 - 0.259 0.128065 4-1/2 - 0.284 (sic) [ 4.5 ] 0.142295 4 - 0.320 0.160082 N.B. unified thread depth is diferent, at 40 tpi for exampe it's 0.015336. Hope this helps looking at the leaves, "depth of thread" in inches seems the most plausible to me. This item would date back to the 50's, I don't believe there was too much metric action in American machine shops at that time. I'd try _measuring_ the depths with a micrometer, but I don't know where to measure to/from. How is thread depth defined? And by the way, who sets the standards on how these things are measured? -- Jonathan Barnes's theorem; for every foolproof device there is a fool greater than the proof. To reply remove AT |
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