1/2" UNF = 1/4" BSP ??

[SlowlyButSurely]

I have discovered by chance that 1/4" BSP fittings will fit the ports on my CAV filter head which I am under the impression is 1/2" UNF. Either the filter head is not what I thought it was or 1/4" BSP and 1/2" UNF are interchangeable. I'm hoping some knowledgeable person can enlighten me.

 

[earlybird]

The 2 threads not too different dimensionally, but certainly not intended to be interchangeable. It is possible however that poorly toleranced items might engage over a fairly short length, especially if the male BSP thread is tapered. Not recommended though, but plenty of sealant may hide the deficiencies.

 

[RivalRedwing]

The delights of thread sizes... how can 1/4" be the same as 1/2"........

I'm sure there is a good reason but...... and engineers are trained to think logically,

 

[scottie]

The delights of thread sizes... how can 1/4" be the same as 1/2"........

I'm sure there is a good reason but...... and engineers are trained to think logically,

Depends on where you measure BSP pipe fittings are measured as the nominal bore of steel gas pipes the other is the Outside Diameter of the fitting
a steel bsp fitting could be forced into the softer alloy filter head ( which is also available in metric sizes ) but would be in advisable

 

[Norman_E]

BSP sizes are based on the pipe bore, not the thread diameter of the pipe fitting, hence 1/4 BSP. The two threads may go together, but are acually different and whilst a 1/2 inch UNF bolt may go into a 1/4 inch BSP nut it really should not work the other way as the BSP thread size has a diameter of .518 inch at 19 TPI, against 20TPI for 1/2" UNF. Whatever can be done with mismatched threads, it will not be perfect or allow more than a few threads to engage, and will rely on sealant to prevent leaks.

 

[Graham_Wright]

You can wreck a filter female thread by using the wrong fitting.
1/4" BSP OD 0.518", 19 tpi
1/2" UNF OD 0.5" 20 tpi.

 

[Aeolus]

BSP thread size has a diameter of .518 inch at 19 TPI

1/4" BSP OD 0.484", 19 tpi

And even the people who reckon they know these things don't always agree.

 

[VicS]

BSP thread size has a diameter of .518 inch at 19 TPI

1/4" BSP OD 0.484", 19 tpi

And even the people who reckon they know these things don't always agree.

1/4" BSP is 0.518" OD according to my Zeus

 

[Graham_Wright]

1/4" BSP is 0.518" OD according to my Zeus

Corrected

 

[SlowlyButSurely]

Thanks very much for all the replies chaps. Mystery solved.