Please help me identify this thread size

[denbigh1974]

I have a heating oil tank which is filled up by connecting to a threaded male inlet at the top. I need a new lockable cap for it. The thread is parallel-sided (i.e. not tapered)

I assumed that the thread would be 2" BSP. Having bought an appropriate cap (SpinSecure) on the internet, however, I discovered that it would not screw on. The cap female thread was too small.

So I measured the tank's inlet thread dimensions using some digital calipers. These dimensions are as follows: Outer diameter (thread crest-to-crest) =3D 60.4mm Inner diameter (thread trough-to-trough) =3D 58.0mm

I estimate the measurement error to be =B10.2mm.

I also measured the distance from the 1st crest to the 9th crest to be

19.12mm so there are eight threads in 19.12mm (=3D 10.63 threads in 25.4mm or 1 inch).

Anybody any idea what thread size this could be?

When I looked up the 2" BSPP date it said Outer diameter (thread crest-to-crest) =3D 59.6mm Inner diameter (thread trough-to-trough) =3D 58.0mm

[denbigh1974]

Oops, that last paragraph should read:

When I looked up the 2" BSPP data it said Outer diameter (thread crest-to-crest) = 59.6mm Inner diameter (thread trough-to-trough) = 56.7mm Threads per inch = 11

[harry]

Pipe sizes (and threads) relate to the bore of the pipe not the actual thread/OD of the pipe.. Even then it's only approximate as there are different pipe wall thicknesses. So 2" BSP steel pipe has an OD of about 2.3" The next size down is 1.5" which has an OD of about 1.75".

Both parallel and taper threads are used for different purposes

It's not bound to be BSP. The BSP thread is a bit coarse for hand tightening and is sometimes not used in such places in the smaller diameters.

Tables here with sizes and pitches.

[polygonum]

Got an Android phone? Try this:

[denbigh1974]

Unfortunately, my thread doesn't seem to be BSPT. Its o.d. is 60.4mm (2=E2=85=9C")

Has anyone else got any ideas?

[Nightjar]

I think it probably is intended to be 2" BSP, as that seems to be the standard size for domestic oil storage tank inlet connectors. Does the delivery driver have problems connecting the hose?

Colin Bignell

[Rick Hughes]

outside diam of 2" BSP is 2 3/8" which is what you have isn't it ?

[Rick Hughes]

in case you want it all ..

Bore of tube 2" OD of tube 2 3/8" Diam of thraed 2.347" core diam 2.231"

11 tpi

sounds to me that is what you have 2" BSP

[denbigh1974]

What's the difference between OD of tube and diameter of thread?

The outside diameter of a 2" BSP thread is 2.347". The outside diameter of my thread is 2.375". Mine is larger than 2" BSP!

[denbigh1974]

Good question. I haven't arranged for a delivery yet but deliveries have been made to this oil tank in the past before my time.

I have phoned around a couple of local oil fuel suppliers but the "engineering" involved in this question is beyond them, unfortunately.

[Roger Mills]

Why is that relevant?

British pipe sizes relate to the *nominal* bore. The thread size is always the same. The *actual* bore depends on the wall thickness, and can vary.

Anyone reading your post might conclude that the bore is always the same and that the OD varies with wall thickness. That would be cobblers!

[Apellation Controlee]

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[harry]

Sometimes they have a hose that just pokes in the hole and doesn't actually connect.

[harry]

It's relevent because some people think that the thread/pipe size relates to the OD not the ID which is variable.. And the ID/wall thickness depends on the pressure rating of the pipe.

[Roger Mills]

It's irrelevant because 2" BSP is 2" BSP and is *always* the same thread size regardless of wall thickness (which the ID isn't). The only thing that's correct in your comment is the fact that the OD of a 2" BSP fitting is actually larger than 2" because the 2" refers to the nominal

- and I emphasise the word "nominal* - bore.

[Rick Hughes]

Probably supposed to be 2" BSP just oversize by 0.028" less than

1/32" difference. Probably just rough manufacture

[denbigh1974]

You're probably right.

I'm going to have to buy an adaptor with a collar that fits over the existing thread converts to a proper 2" BSP male thread.

Thanks to everybody for their assistance.