Here are two more views of the rear sight micrometers for more detail.

The one in the center is imported from England as seen in the lower corner. PJ O'Hare imported a number of target shooting items that were identified with his logo. Bill Brophy referred to that micrometer as a "Convoy" Micrometer in this Krag book?

The Ideal Model cost less but was a bit more difficult to use. They all require about three hands to use them effectively when shooting prone with a good tight sling while the clock is running on the firing line.

The other O'Hare micrometer in the collection is vintage ex military rifle team property. It has been twice marked and numbered "USCG #24". 

As a long time target shooter, I like collecting these crazy little marksmanship items.

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