BSP Internal Thread Lead-In Chamfer?

Did you ever thought about taper Threads -BSPT (Rc1/8") or NPT ? That may sort out the problem. Normally yes, thread chamfer is permitted on the Female threads - but that is specifically to accommodate O rings. (As you are aware the BSP/BSP threads usually need a seal/Oring to arrest the leakage- but that depends on the fluid, pressure and criticality)

Interesting. 30° inside the hole!!?

We're stuck with a flat bottom hole by design. With a metal, tapered, male fitting being inserted in the plastic female threaded part, our problem is with the lead in not (yet) being chamfered, and the assemblers are cross threading about 1 out of every 10 parts. Those have to be scrapped because they won't seal after the cross threadding insult, and the cost is killing us.

We were hoping that either by design specification, or standard machining convention, a lead-in chamfer should/may be added. However, I can't find any literature that says it is permitted or appropriate, and the supplier quality engineer wants us to make a print change which takes lots of time and effort that we'd like to avoid by finding precedent.

Can you help?

Thanks,

Don

WHY? BSP (British Straight Parallel) is one of the worst threads to seal! The Germans used this for years but almost always used some kind of thread sealant. Seal washers and copper washers are also used. See any good Hydraulic spec book about these threads or find the DIN spec., as yes a small lead-in helps to align the threads. The DIN spec will detail ALL ALLOWABLE design parameters.

Additional info: If you are trying to put a brass NPT fitting into a Plastic BSP female you are using two different types of threads. They are close but one is parallel thread and the other is tapered. The BSP thread seals on the flat face when the fitting is bottomed (toppped) into the hole. The NPT thread with proper sealant seals as the taper locks up.

It may be wrong to compare NPT with BSP.

Any thread (NPS or BSP which are equivalent) will need a face sealing

The equivalent of NPT is BSPT and that definitely have an advantage in terms of additional TPIs (ie finer pitch)

The BSP threads are also called Gas Threads and are in regular used in various critical sealing operations, and that includes not only actual gas sealing but also hydraulic lines.

There are certain advantages you gain with the splitting of the two function - holding and sealing as in BSP series- thread is used for the fastening and major sealing function and the rest of the sealing is done by the metallic/ non metallic seal put on the face of the male member.

BTW- Most of the process instrument that we put in our equipment (we specify and procure ) none of these ie NPT of BSP/T they are straight metric - of course fine pitch (eg M33x2, M20X1, etc in thermowells, pressure transmitters etc) and we seal through metallic (copper or otherwise), ceramic or rubber washers on the face depending on service conditions.

The NPT and BSP/T wars are across continent the only difference 55 to 60 dg angle will not improve. deteriorate the sealing and the helical leakage path will remain whatever small if two straight thread mate and in case one of them (or both) are taper, this will be reduced/eliminated by elastic deformation/yield for both the profiles.