hmmm I think that the only real remedy is to redrill it properly to a larger diameter which may or may not impact its function. I'm guessing not many people will have the right tools for this.
Its basically a solid threaded rod of SS, obviously its been drilled from both ends, rather than right the way through, and where the bores meet, they don't line up great. Good thing is its not a barbed item.
Are you able to claim a manufacturing fault from the guys you bought it from ?
I don't think i'd get very far, that's the problem with ordering stuff from the US.
Its only after a good year or so later that I've finally decided that's the problem. Most of my 4 SS shanks have the mismatch in the centre bore, but to varying degrees, the worst is perhaps 0.7 mm out, and is almost unusable without slowing the flow to a dribble, the others work well enough
But definitely a trap for people looking for cheap SS shanks.