BSPT die stock or bolt die: two threads, two tools
Updated: 2026-10-21
A BSPT die stock or bolt die is not one purchase with two names. The ratchet cuts an inch pipe thread. The round die cuts a bolt thread. Neither tool is a gas-pipe project, and 20 mm conduit is a third thread again. Products Compared read the seven amazon.co.uk listings on 19 October 2026 and did not run a lab test. The prices sit on the [die stock comparison](/hub/workshop/die-stock). A qualifying purchase can earn a commission at no extra cost to you.
A BSPT die stock or bolt die is not one purchase with two names. The ratchet cuts an inch pipe thread. The round die cuts a bolt thread. Neither tool is a gas-pipe project, and 20 mm conduit is a third thread again.
A BSPT die stock or bolt die is not one purchase with two names. The ratchet cuts an inch pipe thread. The round die cuts a bolt thread. Neither tool is a gas-pipe project, and 20 mm conduit is a third thread again. Products Compared read the seven amazon.co.uk listings on 19 October 2026 and did not run a lab test. The prices sit on the die stock comparison. A qualifying purchase can earn a commission at no extra cost to you.
Our top picks
| Badge | Product | Type | Thread named | Fit | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  Unifizz Unifizz holder and 1/2-13 UNC die | Round die stock | 1/2-13 UNC | 26–38 mm OD | 6.5 | about £19.56 | View offer |
 ALETO ALETO 20 mm and 25 mm conduit stock | Conduit stock | Conduit; pitch not printed | 20 mm and 25 mm conduit | 7.7 | about £39.99 | View offer | |
| Best value |  BGS BGS 1891 pipe die stock set | Pipe ratchet set | Not printed | 1/4 in to 1 1/4 in | 6.8 | about £26.32 | View offer |
On this page
Two tools, two threads
A pipe die stock is a ratchet and inch chasers, for a quarter turn at a time when the handle would hit the bench. A round die stock is two handles and one circular die, for bar, studding and bolts. Pipe chasers do not drop into that socket, and a bolt die will not cut a sealing thread on 1/2 in pipe.
The BGS 1891, at £26.32, is the ratchet here: 1/4 in to 1 1/4 in, plus an extension bar, stated at 5.66 kg. Unifizz includes a 1/2-13 UNC die, MACHSWON a 3/8-16 UNC die, and the CoCud files include no die. If the piece in the vice is bar, use a round die of the thread on the nut.
BSPT, BSPP, and what the listing must say
Pressure-tight joints on the thread follow BS EN 10226-1, the taper marked R, still called BSPT. Threads that seal on a washer follow BS EN ISO 228-1, the parallel series marked G, still called BSPP. Both are Whitworth form at 55 degrees. A taper in a parallel port can feel tight and still weep. NPT is a 60 degree American taper, not a UK fitting's thread.
Inch sizes alone have not chosen the series. BGS never prints BSPT, BSPP, NPT, R or G, and the title says eight pieces while another line says one. The Sealey PTK991, which does print BSPT, was £89.08 including VAT at ocldirect.co.uk. It is not an ASIN here. The higher price is the printed standard, not proof the cheaper set cuts the same thread.
The £26 set and the round holders
The fifty BGS review bodies are not marked United Kingdom. They warn of broken chasers and a broken handle from about 1 in. Skip those sizes if a broken tooth ends the job, and skip the set if you cannot name R or G.
Unifizz at £19.56 is 1/2-13 UNC, not a metric stud and not 1/2 in pipe. MACHSWON at £3.35 is 3/8-16 UNC, and one UK review says the die came loose and the screws stripped. A pipe die will not cut a metric bolt, and an M12 die will not cut 1/2 in pipe.
Where you stop
Gas pipe is the stop. Regulation 3 of the Gas Safety (Installation and Use) Regulations 1998 makes competence the test, and regulation 22 requires a test and purge where gastightness may have been affected. Gas Safe Register says not to disturb gas-carrying parts. If the pipe might be gas, leave it and get a registered engineer.
Water and heating, with the form confirmed, are the only pipe jobs these listings border. A BSP chaser on 20 mm conduit ruins the box thread. Inch sizes with no R or G have not told you what the BGS die will cut.
Common questions
Will a pipe die stock cut a thread on studding?
No. The chasers cut an inch pipe form, taper or parallel, on tube of that nominal size. Studding wants a round bolt die in a round stock, in the thread the nut already is. Putting pipe chasers on bar tears the crest and will not start a metric or UNC nut.
Will a round M12 die cut 1/2 inch pipe?
No. An M12 die cuts an M12 bolt thread. Half-inch pipe is a BSP series, R or G, and it needs a pipe die of that series. The round stocks in this comparison do not hold pipe chasers. Unifizz and MACHSWON are UNC, which is a third mismatch.
What is the difference between BSPT and BSPP?
BSPT, marked R, is the taper thread to BS EN 10226-1 and is meant to seal on the flanks in a pressure-tight joint. BSPP, marked G, is the parallel thread to BS EN ISO 228-1 and seals on a washer, not on the flanks. Both are 55 degrees. The fitting has to match the die. Tape does not turn one into the other.
Does the BGS set say BSPT?
No. It lists inch sizes from 1/4 in to 1 1/4 in and does not print BSPT, BSPP, NPT, R or G. The piece count also disagrees, eight in the title and one on another line. A kit that does print BSPT, the Sealey PTK991, was £89.08 including VAT and is not in this amazon set.
Can I thread a gas pipe if I am careful?
No. Competence is the legal test under regulation 3, and a test and purge follows if gastightness may change. Gas Safe says not to disturb gas-carrying parts. Care with cutting oil is not that competence. Leave the pipe to a Gas Safe registered engineer.
Why do larger sizes in the reviews break teeth?
The review texts in the BGS file, which are not marked United Kingdom, describe broken chasers and a broken handle once the cut reaches about 1 in, and more play than a trade ratchet. Smaller sizes with oil are the cuts those texts treat as usable. A 1 in die that loses a tooth does not finish the thread.
Is NPT close enough for a UK fitting?
No. NPT is a 60 degree taper. BSP threads are 55 degrees, and R and G still differ from each other in whether they seal on the flank. A die that almost starts in a UK port is the wrong die. Buy the series the fitting is marked with.
Related pages
Sources
Public UK sources used for this comparison. Listings were read on 19 October 2026.
- Accu die stocks and size chart (retrieved 19 October 2026)
- Protool diestocks (retrieved 19 October 2026)
- HSE metalworking fluids (retrieved 19 October 2026)
- MEICA electrical specification, BS EN 61386-1 (retrieved 19 October 2026)
- RoyMech pipe threads (retrieved 19 October 2026)
- Gas Safety (Installation and Use) Regulations 1998, regulation 3 (retrieved 19 October 2026)
- Gas Safe Register, home improvements (retrieved 19 October 2026)
- DETA 20/25 mm conduit stock (retrieved 19 October 2026)
- Technology Student, external threads (retrieved 19 October 2026)