Bayonet Marking Question

Hello:
Can any translation feedback be given on the marking shown on the grip of a Type 30 bayonet? My apologies for the quality of the image and if I have the image rotated incorrectly. I provide images of two rotations. Thank you for any help.

補穴 (unsure if it should be read right-to-left or left-to-right, as was the custom up until the late 1940s.)

I don't know the meaning. I've looked online and couldn't find anything, other than bayonets with similar stamps on auction sites. You might want to try the Warrelics forum in the "Japanese Militaria" sub-forum).

Or @Dentanmono might know something about these bayonets or these marks.

(I should say, I know the meanings of 補 and 穴... the former means "supplementary" or "auxiliary" and the latter means "hole". I just don't know if the stamp should be taken at face value, and read as "auxiliary hole", or if it has another meaning).

Thank you Majestic. Considering that it is a training bayonet, as I have discovered, I thought it might be the name of a school. I will post on the War Relics forum, as you suggest.