Dumb Question: Need A Thread Pitch

[Jim Dandy]

I got a call at 1:30 this A.M. from the local police. Seems some piece of DUNG decided he needed the tag from my '82 300D and took it (we think it happened in the parking garage where my wife works in Oklahoma City). This same bright person, and credit to meth cookers everywhere, managed to get himself stopped somewhere in Kansas where the authorities there determined that his car had a tag that was not registered to it. They then contacted my local police who thought it was important enough to get me out of bed in the middle of the night to quiz me (but they won't tell me where in Kansas this happened).

At a more suitable time (10:00 in the A.M.), I went to a local tag agent and bought a new tag for $12.50 ($12 and some change is not a good enough reason to disturb my sleep). Before I can attach the new tag, I need some hardware to replace what was stolen. My car has threaded inserts. Can anyone give me this pitch? I'm wanting to get some torx head screws to make it tougher on the next bag of dog$hit.

I know it sounds trivial, but humor me. TIA.

[leathermang]

I would go to my local Ace hardware... or that type place...and tell them what happened and ask for help.... typically you get one each of some close and take them out to the car and try them...and then bring the others back and put them into the CORRECT box... so as to not mess up someone elses day who sent the wife to pick up some specific size and she did not check to see what was in the ' 3/8ths ' box.... LOL
Most people , even if they have the same as yours... are not going to know the pitch for a metric thread ....

[Tirebiter]

I get anti-tamper Torx license plate fasteners at Auto Zone, Pimp Boys, and I've seen them at local metric supply houses. I use them on all my vehicles including motorcycles.

I've also seen people fill the cavity of an allen drive bolt with JB Weld epoxy after they tightened it up on the license frame. If they want it off later they pop it with an automatic center punch. Thieves will move on to easier prey.

My father used to attach his plates with phillips head drive bolts and after they were tight he would drill the center of the bolt to remove the slots. To get the bolts off he simply drilled down farther until the head pooped off.

[Jim Dandy]

Originally posted by leathermang
Most people , even if they have the same as yours... are not going to know the pitch for a metric thread ....

Yeah, but I figured a nice guy like you might go outside and check to save me some trouble. Have mercy, I'm a crime victim.

[leathermang]

I have a Cheap 1980 240d...
what are the chances those are the same as your expensive MB?
I will go up front and look at them.... but I don't know if I can tell one pitch from another .... will this be marked on the head of the bolt ? I can determine number of threads on metric... but not sure that is the same thing....

[Eskimo]

Originally posted by leathermang
I have a Cheap 1980 240d...
what are the chances those are the same as your expensive MB?
I will go up front and look at them.... but I don't know if I can tell one pitch from another .... will this be marked on the head of the bolt ? I can determine number of threads on metric... but not sure that is the same thing....

For starters, you can just measure the major diameter of the screw to determine the nominal metric size (M4, M5, M6, etc.). For a lot of things, that will get you there, because for any given diameter (especially with the smaller sizes), only one pitch is commonly used (M6 with a pitch of 1 mm, for example).

Use Google to search for "metric + thread + pitch" if you don't happen to have a chart handy. A very simple chart will do, but if you want lots of information, check with Maryland Metrics. (Nice site, really - see their technical index for lots of information, and also cool stuff like their inexpensive metric thread gauge.) But I digress...

If you wish to confirm the pitch, then you can either use a thread pitch gauge or do the "number of threads" thing you mentioned to figure the pitch (distance in mm divided by the number of threads).


-- eskimo

[Jim Dandy]

Went to Ace after my wife got home and found some Allen screws that worked -- along with some Loctite red. Steal this, F@#$ing Savages!!!

[leathermang]

Thanks Eskimo, I am sure those are good reference sites....I have the charts in my metal working books...
It is only when they throw in the UNcommon pitch that things get bad.... there was one on VW's which was that way.... why they did that I will never figure out...

[Eskimo]

Originally posted by leathermang
Thanks Eskimo, I am sure those are good reference sites....I have the charts in my metal working books...
It is only when they throw in the UNcommon pitch that things get bad.... there was one on VW's which was that way.... why they did that I will never figure out...

I figured it was taking coals to Newcastle to tell you how to figure the pitch of a thread, but I figured that somebody might find it useful. If it's handy, I'll always use a thread pitch gauge anyway, but I've counted threads in a pinch, too.

Do glance over the technical index at Maryland Metrics some time, though - you might find something interesting - "Using USA Coin Measures As Emergency Measurement Tools" ? I have purchased from them, too, when I needed some British Standard taps and dies.

[leathermang]

I post lots of stuff for general consumption.... you never know when someone will see something they did not even know to ask about....

[leathermang]

"TO ESTABLISH THE IDENTITY OF AN UNKNOWN THREAD, CERTAIN TOOLS AND DATA
ARE NECESSARY. INCLUDED IN THESE CHARTS AND DIAGRAMS ARE A HELPFUL
COMPILATION OF THE DATA NEEDED FOR THE IDENTIFICATION OF MOST EXTERNAL
(MALE) THREADS FROM THE THREE MOST POPULAR THREAD SYSTEMS IN THE WORLD,
METRIC STANDARDS, U.S.A.(INCH) STANDARDS, AND THE BRITISH (INCH) STANDARDS.
ALSO THIS CHART WILL OUTLINE THE USEFUL TOOLS AND PROCEDURES IN ATTEMPTING
TO IDENTIFY MANY OTHER UNKNOWN THREADS.

THESE ARE THE THREE BASIC STEPS TO IDENTIFY A THREAD:

STEP 1. MEASURE THE MAJOR DIAMETER OF THE MALE THREAD. THE MAJOR DIAMETER
IS THE OUTSIDE DIAMETER (O.D.) OF THE MALE THREAD. IF YOU ARE TRYING TO
IDENTIFY AN INTERNAL (FEMALE) THREAD THESE DATA CHARTS MAY NOT CONTAIN
SUFFICIENT INFORMATION. FOR ADDITIONAL INFORMATION ON MEASURING INTERNAL
(FEMALE) THREADS; SEE THE INSTRUCTIONS IN CHART VIII.

STEP 2. DETERMINE THE NUMBER OF THREADS PER INCH, OR THE NUMBER OF THREADS
PER CENTIMETER (cm). SEE SECTION (B) FOR CONVERSIONS FROM PITCH TO THREADS
PER INCH, AND/OR THREADS PER CENTIMETER. AN IDEAL WAY TO ACCOMPLISH
THIS MEASUREMENT IS WITH PITCH GAGES OR WITH THREAD GAGES (Note: PITCH
GAGES ARE QUITE INEXPENSIVE). HOWEVER, USING A RULE AND TAKING A CAREFUL
COUNT OF THREADS IS NORMALLY ACCEPTABLE. IF YOU HAVE ACCESS TO THREAD
PITCH GAGES YOUR TASK WILL BE GREATLY SIMPLIFIED.

STEP 3. COMPARE YOUR MEASUREMENTS WITH THE DATA CHARTS IN SECTION (A).


NOTE: CLASS OF FIT - SUCH AS THE U.S.A. '2A/2B' OR THE METRIC '6G/6h' ARE
BEYOND THE SCOPE OF THE DATA INCLUDED IN THESE CHARTS.


SOME HELPFUL NOTES ABOUT THREADS;

1. THE METRIC THREAD DESIGNATION USES PITCH IN PLACE OF THE MORE FAMILIAR
U.S.A. METHOD OF THREADS PER INCH (TPI). PITCH IS THE DISTANCE IN mm FROM
ANY ONE POINT ON A THREAD TO A CORRESPONDING POINT ON THE NEXT THREAD, WHEN
MEASURED PARALLEL TO ITS AXIS.

2. METRIC COARSE THREAD DOES NOT NEED TO HAVE THE PITCH SPECIFIED. THE
ABSENCE OF A PITCH SPECIFICATION INDICATES THAT THE THREAD WILL BE FROM
THE COARSE THREAD SERIES.

3. THE NOMINAL DIAMETER OF METRIC PIPE THREADS, BOTH TAPERED AND PARALLEL
IS THE SAME AS THE MAJOR DIAMETER (O.D.) OF THE THREAD. HOWEVER, THE
U.S.A., BRITISH AND JAPANESE NOMINAL PIPE THREAD DIAMETERS CORRESPOND TO THE
APPROXIMATE INSIDE DIAMETER (I.D.) OF THE PIPE OR TUBE. IN SECTION (A), ALL
THESE THREADS ARE LISTED IN ASCENDING MAJOR DIAMETER SIZE ORDER. THIS PLACES
THE U.S.A., BRITISH, AND JAPANESE PIPE THREADS AMONG THE THREAD DIAMETERS
WHICH ARE LARGER THAN THEIR NOMINAL SIZE.

4. MOST METRIC COUNTRIES IN EUROPE AND ASIA USE THE BRITISH BASED INCH
SYSTEM (ISO) FOR MEASURING PIPE AND TUBING THREADS. SOME EXAMPLES OF THESE
THREAD DESIGNATIONS FOLLOW:

THREADS EQUIVALENT TO BSPP/BSPF (BRITISH STANDARD PIPE - PARALLEL) ARE
DESIGNATED IN GERMANY AS: G 1/4; IN FRANCE: G 1/4 cyl; IN JAPAN: PF 1/4;
IN BRITAIN: R 1/4 Tr.

THREADS EQUIVALENT TO BSPT (BRITISH STANDARD PIPE - TAPERED) ARE DESIGNATED
IN GERMANY AS: R 1/4 keg; IN FRANCE: G 1/4 co; IN JAPAN: PT 1/4; IN BRITAIN:
R 1/4.

THE REFERENCE STANDARDS FOR ISO R228 PARALLEL PIPE THREAD ARE DESIGNATED AS:
GERMANY - DIN 259; BRITAIN - BS 2779; JAPAN - JIS B 0202

THE REFERENCE STANDARDS FOR ISO R7 TAPERED PIPE THREAD ARE DESIGNATED AS:
GERMANY - DIN 2999; BRITAIN - BS 21; JAPAN - JIS B 0203

5. IN THE BRITISH SYSTEM THERE IS NO NEED TO INDICATE THE NUMBER OF THREADS
PER INCH. EACH OF THE BRITISH THREAD SERIES HAVE ONLY ONE NUMBER OF
THREADS PER INCH ALLOCATED WITHIN ITS SERIES AND NOMINAL DIAMETER.

6. THE U.S.A. MINIATURE THREAD SERIES (UNM) IS INTERCHANGEABLE WITH THE
CORRESPONDING SIZES OF ISO METRIC THREADS WHERE THE NOMINAL DIAMETERS
ARE EQUAL.

7. A FEW ADDITIONAL HINTS TO THREAD SYSTEM IDENTIFICATION ARE AS FOLLOWS:
GENERALLY, BOLT HEADS WITH NUMERICAL MARKINGS SUCH AS 8.8, 9.8, 10.9, 12.9;
AND [JIS (JAPANESE INDUSTRIAL STANDARD) NUMERICAL MARKINGS: 7, 8, 10;] WILL
PROBABLY BE METRIC PROPERTY CLASSES; AND BOLT HEADS WITH LINE/SLASH MARKINGS
WILL PROBABLY BE FROM THE U.S.A. GRADE MARKING SYSTEM.


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MEASUREMENT PROCEDURES:

1. BY USING A MICROMETER OR CALIPER; DETERMINE THE MAJOR DIAMETER (ACTUAL
OUTSIDE DIAMETER) OF THE MALE SCREW THREAD. THE MAJOR DIAMETER MAY BE
MEASURED IN DECIMAL INCHES OR MILLIMETERS. NOTE THAT THE MAJOR DIAMETER
VALUE IS SLIGHTLY UNDERSIZED FOR FEMALE THREAD CLEARANCE, BUT THE MAJOR
DIAMETER IS NEVER GREATER THAN THE NOMINAL SIZE OF THE MALE THREAD.
(SEE DIAGRAM III).


2. BY USING A RULE OR CALIPER, DETERMINE THE NUMBER OF THREADS PER INCH.
(SEE DIAGRAM II). OR IF AVAILABLE, A MORE ACCURATE METHOD IS TO USE A
PITCH GAGE OR A THREAD GAGE.



NOTE: TO PROPERLY IDENTIFY A THREAD, YOU MUST HAVE BOTH A DIAMETER
MEASUREMENT AND A PITCH VALUE, OR THREAD PER INCH VALUE.
3. GO TO THE APPROPRIATE SIZE RANGE OF SECTION (A). CHECK THE BASIC MAJOR
DIAMETER COLUMNS; LOCATE THE CLOSEST MEASUREMENT IN EITHER THE APPROPRIATE
MILLIMETER (mm) OR DECIMAL INCH COLUMN FOR THE NOMINAL DIAMETER THAT YOU
HAVE MEASURED IN STEP ONE. MOVE ACROSS THE ROW UNTIL YOU HAVE FOUND A MATCH
FOR THE THREADS PER INCH OR PITCH MEASUREMENT FROM STEP TWO.

4. IF THERE IS ONLY ONE THREAD IN THIS ROW WITH YOUR PITCH OR THREAD PER
INCH VALUE, THEN THE THREAD IS NOW IDENTIFIED. HOWEVER, IF THERE IS MORE
THAN ONE THREAD IN THIS ROW, YOU WILL HAVE TO DETERMINE THE ANGLE OF THE
THREAD FOR A FINAL IDENTIFICATION (SEE DIAGRAM VIII BELOW PLUS DIAGRAMS
IV THROUGH VII FOR THREAD ANGLES). FOR EXAMPLE, A METRIC SCREW PITCH GAGE
WILL READILY SHOW THE DIFFERENCE IN THREAD ANGLES BETWEEN 'BA' (47 1/2
DEGREE) THREADS AND METRIC (60 DEGREE) THREADS.




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(CHART IV): TAP DRILL FORMULA FOR METRIC 60 DEG. THREADS; NOMINAL O.D. OF
THREAD (MAJOR DIAMETER) - PITCH = TAP DRILL SIZE. (Note: This formula will
yield approximately 68% - 77% of thread.) Example: TO FIND THE TAP DRILL
SIZE FOR AN M10 x 1.5 THREAD. 10 (O.D.) - 1.5 (PITCH) = 8.5 mm (TAP DRILL
SIZE).
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(CHART VIII): HOW TO CALCULATE THE APPROXIMATE NOMINAL MAJOR DIAMETER
(O.D.) OF THE METRIC MALE (EXTERNAL) THREAD WHEN ONLY THE FEMALE (INTERNAL)
METRIC THREAD IS AVAILABLE FOR MEASUREMENT.
1. MEASURE VERY CAREFULLY THE PITCH (P) USING A THREAD PITCH GAGE, OR
ANY OTHER TYPE OF MEASURING TOOL WHICH WILL GIVE AN ACCURATE READING FOR
PITCH.
2. MULTIPLY THE FACTOR VALUE: (F)=1.0825 BY THE PITCH (P) WHICH YIELDS
RESULT (R). F x P = R. Example: 1.0825 (F) X 1.75 (P) = 1.8944 (R)
3. MEASURE VERY CAREFULLY THE (I.D.) INSIDE DIAMETER (MINOR DIAMETER) OF THE
FEMALE METRIC THREAD USING AN INTERNAL MICROMETER, INTERNAL CALIPER, OR
GAGE PIN.
4. ADD THE MEASURED VALUE FOR THE INSIDE DIAMETER (I.D.) TO THE RESULT (R)
WHICH WILL YIELD THE NOMINAL MAJOR DIAMETER (O.D.) OF THE FEMALE THREAD.
I.D. + R = O.D. Example: ASSUME MEASURED VALUE 10.1036 (I.D.) + 1.8944 (R)
= 12 (O.D. OR APPROXIMATE NOMINAL MAJOR DIAMETER).

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