How to Measure Thread Depth Without Pitch Guage/three Wire Method or Gauge...

So you need to cut a random thread. May be random O/D or a thread pitch you have not machined before. I use this method for the oddball threads I cut on occasion. If you do not have a pitch guage large enough (or at all) or the proper three wire measuring set here is another way.

So thread cutting for most is a scary operation. Quick hands are needed.
Dont be afraid of the machines!!!
The theory:
Using the thread depth formula is great!!unless you do not sharpen your tool properly. The root ( bottom ) of the thread needs clearance. If you use a shrarp 60° tool the formula will leave you short on your threads.
Every thread pitch has a standard flat on the crest ( top ) of the thread, that is how we are going to measure our depth!!
Formula:
thread depth= 1÷ pitch× .6495
flat of the thread= 1÷pitch÷8
easy right??

So now all you have to do is set your vernier calipers to the number given by the flat of thread formula. Lock them in place. Now use them as a guide to measure the flat on the crest of your thread. This can be a little tricky. If your verniers slide off your flat is to big and your depth is not corrrect. Your vernier should somewhat catch on the crest, that means your depth is very close to correct.

So if you are using a sharp tool you woll probably have to cut a little deeper on your thread passes to get to proper depth and not have any interferance. Be sure to check the type of thread required. Some are sharp V, rounded root and some are standard flat.
It is common practice to grind a flat on tool to meet specs of certain threads. Sometimes a sharp V is preferred because the female thread is unknown so a sharp V should clear most.
This method only works if the ODM is correct.
Hope this helps. Please add anymore info if I am missing something or if another method can be used!! We are all here to learn!!