Odd? US trainer grenade pre wwII?

[JCB99]

Hello all, I collect Japanese but sometimes Non Japanese items catch my eye. I don't know U.S. grenades, can someone tell me if this US training grenade is unusual or different? This seems odd. Can those in the know tell us about this piece?

Thank you!
Jim
JapaneseOrdnance at Yahoo.com

 

[Eugenio]

A training grenade closed by a metal screw? It sounds (to my) so unusual that I recommned to search in other way.

And also the upper part is not as the Mk 1/2