Lock bar clarification confusion

Would someone please tell me which of these descriptions is a Type I, Type II and a Type III? I have a July 1943 M1 with 1,770,XXX serial. My rifle has a square lock bar rear sight on it.

I see only Type II sights described with having rounded bars and Only Type III sights described with square bars. Do the type II have only short pinions and Type III have only long pinions? If so there are 2 types of Type III, square and round.

I'm confused as to what I need to do. Do I need to change just to lock bar to make it correct?

SA Rear Sight Usage

Rear Sight Short Pinion Flush Nut
Checkered Windage/ Checkered Elevation
Used from start of production to 200,000.

Rear Sight Short Pinion Flush Nut
Knurled Windage/ Checkered Elevation
Used from about s/n 200,000 to 500,000.

Rear Sight Short Pinion Rounded Lock Bar
Knurled Windage/ Checkered Elevation
Used from about s/n 500,000 to 1,009,000.

Rear Sight Long Pinion Rounded Lock Bar
Knurled Windage/ Knurled Elevation
Used from about s/n 1,009,000 to 2,700,000.

Rear Sight Long Pinion Square Lock Bar
Knurled Windage/ Knurled Elevation
Used from about s/n 2,700,000 to 3,900,000.

Photos show the first lock bar or Type 1, it was adapted to the short pinion with the 6x40 threads. The Type 2 and Type 3 use the long pinion with the 8x36 threadAttachment 15948Attachment 15949

Quote:

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Originally Posted by mjkberg

I see only Type II sights described with having rounded bars and Only Type III sights described with square bars. Do the type II have only short pinions and Type III have only long pinions? If so there are 2 types of Type III, square and round.

I'm confused as to what I need to do. Do I need to change just to lock bar to make it correct?

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Only the T1 lockbar works with the short pinion. The T2 & T3 lockbars work with all long pinions.

All you need to do is swap the T3 lockbar on your rifle for a T2 to make the rear sight correct.