Advice on Tapping Mishap

All ( most good quality ) taps have a GH after the size . Each H is = to .0005 oversize . Check your tap . ;)
 
The photo shows not a real thick thread engagement.

Still suggest making a test block with your tap, but now add to make it same thickness.

There are instances where metric and sae threads are just that close where they may interchange.

A 10-32 is slightly smaller than the metric one so metric goes in just a couple turns but loose fit other way.

You may find something that goes in and works.

Your photo also shows them as through bolts.

A nut can go on top to add additional strength.




Sent from my SM-G781V using Tapatalk
 
All ( most good quality ) taps have a GH after the size . Each H is = to .0005 oversize . Check your tap . ;)
I thought about that but the H number would not account for .3mm oversize would it? That is .012" over. Even an H7 is only .0035" over?

BTW People might like this:

Class of Threads, H Limits​

Classes Of Threads
There are (3) established Classes of Thread, designated in the unified series by adding: "A" for Screws and "B" for Nuts (or other intenal threads) to show definite limits and tolerances.
Class 1B Thread
Is wherea 1A screw can run in readily for quick and easy assembly. The hole is classified as 1B. The fit is a 1B thread, (very seldom used in modern metal working)
Class 2B Thread
Consists of a 2A screw in a 2B hole. 2B thread has wide applications. It is used to accomodate plating, finishing and coating to a limited extent and threfore, has fair tolerance allowances.
Class 3B Thread
3A screw in a 3B nut or internal threaded hole, used where tolerance limits are close.
GH Numbers
GH Numbers are listed below. "G" designates Ground Thread. "H" designates the pitch diameter is on high side of basic. These two letters (GH) are followed by a numeral indicating the Tolerance of Pitch diameter oversize.

H1=Basic to Plus .0005
H2=Basic Plus .0005 to Plus .0010
H3=Basic Plus .0010 to Plus .0015
H4=Basic Plus .0015 to Plus .0020
H5=Basic Plus .0020 to Plus .0025
H6=Basic Plus .0025 to Plus .0030H=Above Basic
H7=Basic Plus .0030 to Plus .0035L=Below Basic

Relation Of Tap Pitch Diameter to Basic Pitch Diameter
American Tap Manufacturers use a series of tap pitch diameter limits. These limits feature a .0005 tolerance in tap sizes #0 Thru 1" and a .001" or greater tolerance in tap sizes above 1" thru 1 1/2" diameter.
Example: 1/4-20. Relationship between Tap Pitch diameter limits and basic nominal pitch diameter.

Basic

Pitch Diameter: .2175
GH5
----.2200
GH4
----.2190
GH3
----.2185
GH2
----.2180
GH1
----.2175
GL1
----.2170
 
I thought about that but the H number would not account for .3mm oversize would it? That is .012" over. Even an H7 is only .0035" over?
Hard to say what is going on here Robert , the post is confusing as written . :) Not exactly sure which diameter is oversize , minor , pitch or major . He can heli-coil it or Keensert it pretty easily though .
 
Other than heli coils I would be concerned with how much metal would be removed from the flange
For the other type of thread inserts.
I have been installing heli coils for over 35 years and I have never had a failure.
 
This thread has encouraged me to look at the H numbers of my tap collection. All most all of them are H3 (.0015 over). I have one random 10-32 H11. Always learning something from these troubleshooting threads!
 
H3 is basically the standard tap for general purpose class 2 threads . That H11 tap . I use them when making dies knowing the tapped holes will be locking up on the bolts . Half the time it doesn't matter . I still have to mill them out with a carbide end mill , ream to .249 then press in some 303 stainless . Tap them back to the 10s or 8s threads whichever they may be . When the bolts lock up now , I just press the stainless out , and replace . The dies don't see the EDM machine anymore . :)

This thread has encouraged me to look at the H numbers of my tap collection. All most all of them are H3 (.0015 over). I have one random 10-32 H11. Always learning something from these troubleshooting threads!
 
Also beware any taps that say "STI"!

A tap marked "1/4-20 STI" is NOT for threading a 1/4-20 hole!

STI = Screw Thread Insert
These are the over-size taps for installing Helicoil and similar thread-repair inserts.

I like to store them over with the thread inserts, NOT in the drawers for the regular imperial and metric taps and dies.

Brian
 
The UN thread series is defined with a flat at the crest and root. Some taps are ground to a sharp V. The OD of these taps will exceed the specified OD for male thread.
Probably the best solution will to tap a hole in a test block and use that hole as a gauge to select a fastener that fits.
There is a chance you tapped an 8mm thread. If you are lucky that is what happened. Try an 8mm bolt in that hole.
An 8mm coarse thread nut will screw onto 5/16 bolt but an 8mm bolt will not screw into a 5/16 nut.
 
Also beware any taps that say "STI"!

A tap marked "1/4-20 STI" is NOT for threading a 1/4-20 hole!

STI = Screw Thread Insert
These are the over-size taps for installing Helicoil and similar thread-repair inserts.

I like to store them over with the thread inserts, NOT in the drawers for the regular imperial and metric taps and dies.

Brian
Uggg. I fell right onto this trap even after reading this. Dementia sucks.
R
 
Back
Top