I have a 61 capillary filler that has a breathing hole in the side of the barrel. I have seen others, though, without the hole. It doesn't seem to serve any function, since the end of the filling system is sealed at the end of the barrel.
Did this hole exist in the original 61, or was added in the Mark II version?

All my P61's are UK made, which may make my results different from US made ones.

I have a black MkII capilliary P61 Custom (well, I think it's a MKII as the connector ring is about 1mm wide with a Vee groove rather than a narrow sliver which I associate with the MkI). The barrel has a '61' imprint on it. There is no breather hole.

I have a Carribean Green MKII c/c P61 with a Lustralloy cap (and missing silver arrow), no imprint on the barrel, and no breather hole.

Neither my c/c Flighter (MkIII) nor my c/c Insignia (MkII) have breather holes either.

I looked at my wrecked burgundy c/c MKIII P61 Custom, and that barrel is devoid of a breather hole.

So, the presense of a breather hole baffles me.

Regards

Richard.

My US-made 61 Mark I has a tiny hole in the barrel about two-fifths of the way from the jewel to the connector ring. To what purpose I cannot speculate, but it's there.

It's funny, I never really considered the breathing holes. It doesn't seem to have to do with the country of manufacture or the age of the pens.

I have four 61's: two UK custom (both mark I, one India black, one gray) with breathing holes.
One surf green Classic, mark I, US made, without hole
finally, a US made mark II Flighter with a breathing hole!

The presence of the holes doesn't seem to make sense. In any case, all four write equally well!

Evidence of attack by the Parker 61 beetle borer. Unfortunately, your pen is now worthless.