Haven’t seen anyone mention it yet so here’s my unfortunate experience: a lot of low quality Chinese import parts marketed to the cannabis industry has “NPT” threaded parts that don’t actually match the NPT spec for whatever size it is. Usually these are threaded straight, which is to say that a 1/4" NPT/pipe fitting should be 18 TPI (threads per inch) with a .055" pitch taper that gets smaller as the threads get deeper (opening side) and smaller towards the end (pipe side).
Usually what happens - and I suspect this is because metric threads effectively never have a taper and often metric fittings that need to seal tightly do so with a dovetailed O-ring or face seal - is they get cut on a CNC and instead of cutting 1/4-18 with a taper, they just cut the 1/4"-18 threads straight down with no taper, which means that your fitting will never get tighter as it threads in, and you will be reliant on the taper of only one half to do all the sealing work - and on some fitting there simply isn’t enough threads to get big enough to do so effectively.
Your options are then to either drill a larger hole, tap it correctly (if in stainless, this will take a much better tap and lube combo than most people are willing to buy) and then either use a reducer bushing or buy a new fitting to get from the new hole size to whatever you’re trying to connect to. Other option is welding.
I’m out of country til end of the month but if you’re near Denver I could certainly help with retapping it to the correct taper. Nothing should take 8 turns of quality tape, and Blue Monster is good stuff - nothing like the thinner-than-rice-paper-thin white garbage that gets thrown in with most import equipment.