What Is It?

[In Utopia]

On the right front side of my L175 block just above the oil pan there is a plug.
There is a slight oil drip that I'd like to fix.
Here is the Kubota number 15221-33752.

Started to unscrew it, but oil started to come out.
Question is, what is the purpose of this plug? Did it have something to do with casting?

 

[meanjean]

I have multiple bolts as well on a similar machine, L1801.
I'm confident they are strictly for the build process.

 

[ipz2222]

Many oil passages are drilled in blocks. To make 2 passages intersect, the hole is drilled thru from the outside. The outside hole is then plugged or a tap plug is installed.

 

[North Idaho Wolfman]

Another possibility is that is a port for an optional device or accessory, like oil feed for a turbo, or something like that.
Kubota engines are used for a bunch of different uses and some times they just need some thing different than what your tractor needs.