Cool shirasaya mechanism

[Fuuten]

Hi everyone,

 

Checking Aoi auctions I came across this yari which has a shirasaya with some kind of closing mechanism. First time I've seen this. Anyone with more information on this type of thing? 

 

Video

 

https://www.aoijapan.com/katakama-yarionomichi-ju-sonokawani-kunimasa/

 

 

[Bugyotsuji]

For shirasaya.

I once had a Jumonji Yari with two locking pegs for under the cross pieces. Also I had a kusarigama with a locking peg. Neither had that nice hinge idea though.