Tapping puzzler

I'm making a brake line tee for a guy , and I'm having trouble getting an acceptable fit . The compression nut reads 9.85 mm x 1mm pitch . The tap I
bought measures 10.10 ... and the nut is way too loose in the threads . I'm wondering if this auto parts store tap is oversize ... might be OK for a bolt thru a bracket or something , but I'm not using it for this job . Is there a chart somewhere that has size data for taps by fit class ?
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On 7/13/2013 9:39 PM, Terry Coombs wrote:

Flare fittings should be used for brakes, not compression.
MikeB
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For a brake line its typically a double flare fitting. Also, amazingly enough if you "over" tighten them they are more likely to leak then if you under tighten them.
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Yup , double flare . Looks like a little button on the end of the tube . Bob , you wouldn't happen to know the included angle of that seat ? Looks like a 135 deg bit would work , 118 is too steep , it only contacts on the outside edge . I can grind a bit to any angle in between , thanks to my neighbor . <He gave me a DD500X for fixing his older model.>
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wrote:

Do yourself and the guy and just BUY the proper brake line tee. Standard Weatherhead fittings are readilly available.
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Wasn't my idea to begin with ... this is for my neighbor , done a fair bit of work for him already . I do want this done right .
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Terry Coombs laid this down on his screen :

Get a Professonal made part. If you make it and fails you will never hear the end of it.
I had an amature job fail on a brake line 400 miles into the desert north east of Alice Springs a long time ago. That was no fun. :/ Fortunatly there is very very little traffic out there. And I had to make a new flare with a Phillips screwdriver to get home!!! It had been made by the previous owner,before I bought the vehicle. :-Z
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wrote:

You are working on a "critical safety system". "doing it right" generally involves using parts made and certified for the purpose..
Buy the correct brake part for thr job. This coming from a licenced auto mechanic and a machinist.
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wrote:

Nope, that's a compression fitting. http://tinyurl.com/pz9afu5 25 seconds into the video, you'll see the brass sleeve/button.

Terry, I'm not sure you have the proper picture on the task. Here's the picture for a double flared tube. The seat must be a convex shape, not concave, so the bit will have to have a cone rather than a point. http://tinyurl.com/o9mxa69 And the nut will have an inner flare to the tip to mate the bell of the tube.
When I was wrenching, I only saw the Japanese style, not the Euro. http://tinyurl.com/pnhvbdo Which is the one you're working on?
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The ISO/DIN or bubble flare in your link below <and I have an M10 x 1 tap , but it cuts an oversize thread - which is the whole problem here>. The vehicle in question is a Ford Mustang , late model <90-something , I think> . He's putting a different master cylinder on because he's using a rear axle with disc brakes , and I'm also making an adapter plate to mount that .
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Snag

"Larry Jaques" < snipped-for-privacy@invalid.diversifycomm.com> wrote in message > When I
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wrote in message > When

The most likely cause of the problem is that it might not be a metric fitting but a more common 3/8-24 fitting. The 3/8 has a smaller major diameter but is so close to the metric that the 3/8-24 will thread into a 10-1 (not suggested) but the 10-1 will not fit into a 3/8-24 hole.
Paul K. Dickman
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wrote in message >

Nope , this fitting will not thread into a 3/8-24 hole - though some of the lines he's got must , as the proportioning valve he brought down has 2 holes threaded for it - but those also have the conical flare seat , not the concave "bubble" flare . The nut that goes in this fitting <on the 1 piece of tube I've got for fitment purposes> measures 9.85MM and the thread profile matches exactly with the tap I bought . As I said , this tap cuts an oversize thread , it measures 10.11 MM . Allowing for truncated thread profiles , the tap should measure just UNDER 10MM , not over . -- Snag Thanks to Larry Jacques , I now have a drawing of the flare , and can match the seat profile exactly .
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wrote:

The OD of normal taps is always larger than the nominal thread size. Look at the thread tables in Machinery's Handbook and you'll see that the major diameter of internal threads is the nominal diameter with a plus tolerance.
10.11 mm OD for an M10x1 tap sounds about right.
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    And what you want to do to check the diameter of threads is to measure the *pitch* diameter -- which is usually done on male threads with three wires of selected diameter down in the Vs -- two on one side and one on the other. This measures the surfaces which should mate.
    The drawing below should be viewed with a fixed pitch font like Courier. Any of the variable pitch fonts will cause the later (right-most) parts to fall out of alignment on your screen.
~~~~~~~~~~ | | <-- micrometer anvil |________| /\ /\()/\()/\ /\ /\ /\ /\ / \/ \/ \/ \/ \/ \/ \/ \
/\ /\ /\ /\ /\ /\ /\ /\ / \/ \/()\/ \/ \/ \/ \/ \ _________ | | | | <-- Micrometer spindle | | ~~~~~~~
The above shows how the wires should be placed, but they should be a little bigger than shown (limits of ASCII graphics), so they project above the thread crests. Then your micrometer can give you a precise reading which can be converted to the pitch diameter by subtraction of a constant which you look up.

    Yes -- this makes a sharp V crest to the internal threads, to clear any reasonable shape of crest on the mating threads -- Sharp, flat-crested, or rounded.
    Good Luck,         DoN.
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wrote:

But not sharp sharp, just sharper than the mating external thread.
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wrote:

There is something wrong with your logic. Ignoring the question of what fits what I believe you will find that all taps cut a larger diameter then the nominal size of the fastener. If, for example you were to thread a 10 mm rod in the lathe and than drilled and tapped a 10 mm hole the male rod, being 10 mm must be threaded into a larger hole, otherwise it would be an interference fit and damned hard to screw in :-)
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This one is easy to check. I measured a few 1/4" and 3/8" Greenfield taps at 0.0015 - 0.002" under the nominal diameter. jsw
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On Sun, 14 Jul 2013 22:06:34 -0400, "Jim Wilkins"

Then they won't cut proper UN threads. The *minimum* major diameter for 1/4-20 UNC - 2B (and 1B & 3B) internal threads is .2500. Likewise, the minimum major diameter is equal to the nominal size (the basic major diameter) for all 1B, 2B and 3B UN threads. Similar rules apply to metric threads.
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wrote:

OK, many of my tools were second-hand. New 1/4, 5/16 and 3/8 taps measured 3-4 thousandths over nominal size. jsw
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On Mon, 15 Jul 2013 08:34:06 -0400, "Jim Wilkins"

You got me wondering so I checked some taps I have that are old enough to be marked "USS." USS threads were superseded by National (NC, NF) threads, which were in turn replaced by UN threads. Even the USS taps I checked, which happened to be Greenfield taps, had a major dia greater than nominal. What I don't know, because the oldest MH I have covers only National threads in detail, is whether the USS standard insisted on the oversize major dia.
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