Mystery Thread

[barkersegg]

I need to make some plugs to fit a couple of half filled old oil drums - I think they are probably 20 gallon drums by the size - not sure exactly but they are quite old and I have just kept topping them up over the years - never bothered to take their taps off until now as I need to move them and don't want to run the risk of snapping them off if I knock them.

The taps/outlets appear to be made from die cast - probably aluminium and there are two different styles...the normal cock valve type as per the big plastic water containers and the older T valve type.......all threads are the same size.

No dramas to knock up some plugs to fit the drums but the thread on the old taps measure 1.019" x 14tpi.......cannot find anything similar in any charts or books I have so wondering what they are...........

Incidentally, some recent kero drums I had almost fitted the same tap threads - worked good enough with some hemp packing but these would be imperial threads - not sure the form....whereas the kero and modern oil drums would be metric

If anyone else has come across this size before perhaps they can let me know as any help greatly appreciated tks............Barkers.....

[pipeclay]

I would take a punt and ask is the thread parrallel or tapered,try if you like a 3/4" bsp or npt plug,probably easier to find a bspt or bspf plug,if it is npt for what you want to do the bspt or bspf plugs would be ok.

[Woodlee]

No mystery ,its either a BSP (British Standard Pipe thread) or NPT ( National Pipe Thread).
If the drums are old then I'd place my money on BSP.
I reckon as Pipeclay said 3/4" BSP.
Should be able to get gal plugs at the local hardware.

Kev.

[barkersegg]

Thanks Woodlee and Pipeclay - had thought by the fact they were 14tpi that they were most likely BSP or maybe ANP - that was my logic also....great minds think alike eh ...it is the measured OD that has thrown me......my charts for BSP only indicate a 31/32 and then the next size being 1 1/8" - nothing in between with the closest 1 1/8 too big seeing the measured OD is 1.02 and that's 125 thou smaller than 1 1/8......granted, some of my cut threads are pretty rough ......but that's a little too big to work

They are a straight parallel threads - not tapered

It's no problem knocking a couple of plugs up to fit - just that I would had liked to have known what the buggers were....and then keep my good eye out for some replacement taps if/when I break one of these.......rather than stuff around making adapter sleeves...

Thanks again for your input...greatly appreciated

[joe greiner]

Had me scratching the brain too. But the measured size of 1.019 is only a few thous smaller than 1.034/1.024. From a footnote in Machinery's Handbook (ref ANSI B1.20.1-1983), "As the ANSI Standard Straight Pipe Thread is maintained, the major and minor diameters of the internal thread and the minor diameter of the external thread vary with the pitch diameter ... and it should be understood that commercial pipe will not always have these maximum major diameters." If it were me spending your money, I'd bet on 3/4-14 NPSM. And to reduce leaking, add a soft washer or o-ring for insurance.

Joe

[barkersegg]

Thanks Joe, must admit its a strange size and fit - only explanation I could offer is that the taps were cut crudely in die-cast material and that accounts for the size difference in an NP form......I will cut the bungs to fit out of some Delrin and then pack them out to stop leaks if need be........luckily the drums only contain HYPO 90 gear oil and some lighter headstock oil which won't seep..........tks again for your help