Questions on Gear: -80% Thread Mill Only

Looks like 'Lathe Lead-screw's Split Nut' or one of such applications.

'30° lead Typ' could be helical thread's angle and '80% Thread' could be 'recommended thread coverage' since the nut is split and is not continues.

This is a weird drawing. A and B are redundant, and no value is given for them. Neither the inner nor outer dimension is given for the internal threads. All of the terminology in the red box appears to be unusual, or maybe some kind of in-house shop talk.

I would read this as having a 30° chamfer "lead" and 80% engagement, produced by thread milling as opposed to tapping. This is only my interprtation, of course.

Unable to make out the drawing (visualise it)

What is the gear type? I assume it is worm ?

BTW is it a gear?

As far as A and B are concerened, as mentioned in a previous thread, these details may be somewhere else in the drawing. The OP has only reproduced a part of the drawing. There will be other sections and views.

As far as I can get from this

The lead angle portion is clear (if it is worm)

The 80% thread length is the minimum length over which the worm thread is fully formed.

And the thread is formed by milling (why only? is it a shop drawing? is it to clarify that the finishing is to be done in the milling stage itself, no subsequent grinding/ flank correction will be carried out? )

_{All above are assumptions based on what I could understand guess from the data provided. And may be as well going tangential.}

I concur with MusicAl. A 30 degree chamfer "lead" for first thread and 80% engagement - or 80% of a theoretical full thread depth. And of course using a thread milling process.