Does the barrel extension index pin extend into the threads on the barrel or just the barrel extension?

I just bought a pistol caliber barrel extension from Olympic Arms and the index pin was already installed and the hole for the pin is not drilled all the way through the extension. Are barrels just torqued to the extension or is the pin supposed to extend into the barrel threads to keep the barrel from loosening?

The index pin does not extend into the threads. The index pin just touches them. The barrel extension is torqued to the barrel very tightly in a barrel vise. Charles the Gunsmith.  

I appreciate it, Thanks.

I've seen some (one or two) that extend into the threads.  Are they supposed to?  I don't really know, but I wouldn't assume that they do or don't.

Be best to have the pin sink into the threaded portion, effectively locking the works together, just like pinning a muzzle device.  There really is not enough thickness to the  extension collar  to support the pin.  

Article written by American Rifleman editor C E Harris in regard to USMC Match rifles states :

-- Use the hole in the extension as a guide to drill about .010" into the barrel, so that when
the new pin is in place it will prevent loosening of the barrel extension. --