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| mklotz:
Just a note... The formula major diameter = 0.060 + N * .013 [N = screw number] works for the sub '0' sizes as well if you use negative numbers for N. 00 => N = -1 000 => N = -2 0000 => N = -3 So, for example, the major diameter for a 00-90 thread is: MD = 0.060 - 1*0.013 = 0.047 Numbering screws is an idiotic nomenclature (the sensible way is to label them by size as in 1/4-20) but at least in this case there is a formula for the relationship. Formulae are easier to remember than a long list of equivalences. |
| Russel:
I had to do some looking on the net to find references to 00 thru 0000 sizes. The Machinery Handbook starts the sizes at 0, I looked in mine, edition 22 and my Dad's, edition 11. Finally found the itty bitty sized on the net. It is interesting that wood screw sizes follow the same scheme up to size 24 for the shank diameter. |
| mklotz:
Nomenclature for a series of things like screws (machine or wood) or drills should follow certain rules... The system should be open-ended at each end so that, should a smaller or larger size evolve, it can be fit into the sequence without the need for idiocies like 0000-160. It should follow a natural progression, i.e., smaller numbers/letters should denote smaller sizes, and v.v.. The system should provide immediate information about the size without the need for laborious decoding. Applying those rules, it's easy to see how flawed numbered screw and drill designators, letter series drills and wire and sheet gage numbers are. Though it's not part of the SI, in the metric-using world, most things are labeled with their size. This is about the only nomenclature system that agrees with the rules above. |
| andyf:
--- Quote ---Marv: Though it's not part of the SI, in the metric-using world, most things are labeled with their size. This is about the only nomenclature system that agrees with the rules above. --- End quote --- Tho' I'm no particular advocate of the metric thread system, it does have its advantages. Even my mathematical ineptitude can cope with working out the tap drill size by subtracting the thread pitch from the major diameter, like for M5, where 5mm minus 0.8mm = 4.2mm for the tap drill. Andy |
| mklotz:
Works in the (hack, spit) Imperial world too, Andy. For example, a 1/4-20 thread: 1/4 - 1/20 = 4/20 = 1/5 = 0.20 Then, of course, because of the screwy drill nomenclature, one has to consult a chart to determine that the drill closest to 0.20 is a #7 or #8. |
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