What size rod

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What size rod do I use for 8-32 threads.I tried 3/16 but it is too big. thanx

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--Well a clearance drill is 11/32" so it's probably a little below that. Look in the Handbook tho for the correct dia to turn that down to before attempting to thread it..

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--Oops! Misspoke; not 11/32 but 11/64"!!

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The major diameter for #8 threads is .164" #10 is .190" Randy

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For home/hobby low-stress application, 5/32" dia. rod for #8 threads would be OK. For #10 threads 3/16" dia. rod is acceptable. #5 thread is .125", ie. 1/8" diameter.

The rule for # thread outside dia. is quite simple: Begin with #0 thread which is .060" diameter. The steps between thread numbers are a uniform .013".

For example consider #5 thread: .060 + (5 x .013) = .060 + .065 = .

125". Another, say #10 thread: .060 + (10 x .013) = .060 + .130 = .190".

In fact the outside dia. of a screw thread can be considerably smaller than the theoretical requirement. .005" undersize on smallish screws, .010" on somewhat bigger, and .015 0n 1/4" dia. and up. A quick review of the tolerance tables of screw threads in Machinerys Handbook will disclose the standard tolerances. For home/hobby use larger tolerances may be acceptable.

Trust this helps.

Wolfgang

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Outside diameter of 8-32 is 0.1640", so turn the 3/16" down a bit and you're there.

Mark Rand RTFM

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According to Sofolatris :

Well ... the simplest way to f ====================================================================== izalco:dnichols 18:26:43 > number-screw 8 32 For a #8-32.000 screw: Clearance diameter: 0.164 Tap drill diameter: 0.133 ======================================================================

so I would turn to about 0.162" or perhaps 0.160".

I would also be more likely to use the lathe to do the threading, as it is easier to get the threads straight and concentric. You might use the die to finish up threads which are not quite deep enough, as this will at least make it easier to start the die straight.

Good Luck, DoN.

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This may sound like nitpicking, but .164 is the *nominal* size of a #8 screw thread. The *major diameter* (the actual diameter at the thread crests) is determined by applying an allowance to the nominal diameter to insure interchangeability. Major diameter for a 2B thread is .1571 to .1631, which is the number the OP is looking for. As has been mentioned, 5/32 is close enough, 4mm would fall in the spec.

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OK, if you want to pick nits........ :) This chart shows all of that

Randy

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What's a few nits between friends? (Other than the origins of polite society - you delouse me and I'll do the same for you.)

Machinery's Handbook lays it out as well, complete with definitions, pictures, and the logic behind it all.

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All this mental badminton and mental masturbation is fun, but it's hard to beat a good book of facts.

Steve

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Don sez:

"Well ... the simplest way to find out in your shop what size is to look in a number size drill index, and see what the "body" drill is for the thread in question, and turn the rod (in your lathe) a couple of thousandths or so smaller"

Great advice, Don. Turning the rod "a couple of thousandths or so smaller" can be problematical, particularly in the smaller sizes; and even more so when threading with a die. (Harold Vardos - please disregard. You taught me better but sometimes I backslide)

Check in Machinery's handbook for Standard Series and Selected Combinations, usu. picking Class 2A. A good formula for Class 2A is:

Major Diameter = ((1.10825) / (# threads per inch))

Bob Swinney

====================================================================== izalco:dnichols 18:26:43 > number-screw 8 32 For a #8-32.000 screw: Clearance diameter: 0.164 Tap drill diameter: 0.133 ======================================================================

so I would turn to about 0.162" or perhaps 0.160".

I would also be more likely to use the lathe to do the threading, as it is easier to get the threads straight and concentric. You might use the die to finish up threads which are not quite deep enough, as this will at least make it easier to start the die straight.

Good Luck, DoN.

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Slight typo: Replace = sign with minus sign in the formula below:

Make that: Major Diameter - ((1.10825) / (# threads per inch))

Sorry 'bout dat.

Bob Swinney

"Well ... the simplest way to find out in your shop what size is to look in a number size drill index, and see what the "body" drill is for the thread in question, and turn the rod (in your lathe) a couple of thousandths or so smaller"

Great advice, Don. Turning the rod "a couple of thousandths or so smaller" can be problematical, particularly in the smaller sizes; and even more so when threading with a die. (Harold Vardos - please disregard. You taught me better but sometimes I backslide)

Check in Machinery's handbook for Standard Series and Selected Combinations, usu. picking Class 2A. A good formula for Class 2A is:

Major Diameter = ((1.10825) / (# threads per inch))

Bob Swinney

====================================================================== izalco:dnichols 18:26:43 > number-screw 8 32 For a #8-32.000 screw: Clearance diameter: 0.164 Tap drill diameter: 0.133 ======================================================================

so I would turn to about 0.162" or perhaps 0.160".

I would also be more likely to use the lathe to do the threading, as it is easier to get the threads straight and concentric. You might use the die to finish up threads which are not quite deep enough, as this will at least make it easier to start the die straight.

Good Luck, DoN.

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I'm not one for memorizing things so what I do is merely pick up a 8/32 screw and measure it. Now you have the major diameter.

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