What is this on the front forks?

[NCAmother]

Here’s a picture of the lbottom of the forks on an old Tonti guzzi.   In the picture what is the socket head bolt for?  The bolt is facing the front of the forks

[jrt]

Drain plug.

[NCAmother]

Thanks!
One other Question:  what size are the axle pinch bolts?

[turboguzzi]

but just as important is the empty hexagonal cavity under it.... its for the nut of the axle clamping bolt! by the dust in it, someone has been riding without it for a looong time. not safe, not good.

[Antietam Classic Cycle]

Thanks!
One other Question:  what size are the axle pinch bolts?

M10 x 40.

[Stevex]

That pinch bolt is a Allen bolt, with a domed nut in the the pictured recess.

[John A]

Do not over tighten the axel pinch bolts or it will crack the fork leg. It’s a place a torque wrench is will get you in trouble. Especially true on the side with the larger diameter of the axel. Don’t ask how I learned that..