Type 89 Mortar Round Opening

[Bobby]

Hello. Is the square opening at the top of this Type 89 mortar round typical of original manufacturing? If yes, what purpose did it serve?

If not, why would it have been added?

Thank you for any feedback.

[Geoff Ward]

Hello Bobby, Typically these type of openings appear on the Type 100 mortar rounds. They are made to fit a type of Spanner wrench used to tighten the top section of the round, which the fuse screws into. From what I understand this type of round could be used with both an ‎Artillery style impact fuse or a time delay fuse. Here are a few pics from my collection.

[Nick Komiya]

Unscrewed

[Bobby]

Thanks Geoff!

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Thanks Nick!