What BSP Grease Fittings Are
BSP grease fittings are grease nipples, also called zerks, cut with British Standard Pipe threads. The thread form is the 55 degree Whitworth profile, a rounded crest and root that seats differently from the sharp threads used on other systems. These fittings are standard on equipment built to British or Commonwealth practice and on much European machinery, so they appear on presses, conveyors, pumps and machine tools that were never intended for inch pipe threads. They are made in inch sizes from 1/8 to 1/2, each with a matching thread count per inch. A fitting threads into a tapped hole in a bearing housing, a shaft end or a grease line block, and the head accepts a grease gun coupler.
BSPT and BSPP Thread Forms
BSPT is the tapered form, written R on many drawings. The diameter shrinks along the thread at 1:16, so the joint tightens as it advances and the flanks seal against each other; a sealant fills the micro-voids left in the spiral. BSPP is the parallel form, written G. The diameter is constant along the thread, so it cannot seal on the flanks. It seals at a face instead: a bonded washer under the hex, or an O-ring in a machined port. BSPT suits permanent joints and points exposed to vibration, because the taper holds the fitting in place. BSPP suits joints that are opened for service, because the fitting unscrews cleanly and the face seal is renewed with a washer. A BSPT male threaded into a BSPP hole binds after a few turns without sealing.
Sizes and Threads
The table lists the four common sizes with their thread count, major diameter, hex across flats and overall length. Nominal size names the pipe bore history, not the thread diameter.
| Size | TPI | Major diameter | Hex | Length |
|---|---|---|---|---|
| 1/8 | 28 | 9.728 mm | 8.0 mm | 15.5 mm |
| 1/4 | 19 | 13.157 mm | 11.0 mm | 18.0 mm |
| 3/8 | 19 | 16.662 mm | 14.0 mm | 21.5 mm |
| 1/2 | 14 | 20.955 mm | 17.0 mm | 24.0 mm |
For a single size in depth, see 1/8 BSP grease nipples or the dedicated 3/8-19 BSP grease fittings page.
Materials
Brass is the general-duty choice. It resists corrosion in ordinary plant air and wash environments, machines cleanly and does not gall badly in a brass or steel port. Stainless 316 is for marine decks, chemical washdown and high temperature points where a plated fitting would pit or discolor. Zinc-plated carbon steel covers general industrial use where mechanical strength matters more than corrosion resistance. The three are not interchangeable in service life, only in thread. Match the material to the environment the fitting sees, not to the machine frame. See the stainless steel grease nipples family and the metric DIN-style grease nipples family for those variants.
Head Styles and Angles
Straight heads are the default and work wherever the coupler can reach the point along the fitting axis. A 45 degree head and a 90 degree head reach recessed points or points blocked vertically by a frame member, a guard or another fitting. Button head fittings pass higher flow and suit centralized lines and quick couplers. Choose the head by the approach angle the grease gun can actually take, not by habit. A straight fitting behind a cross member is unreachable; the same point with a 90 degree head is a one-hand job. Order the angle that fits the machine, then keep it consistent across the lubrication schedule.
Working Pressure and Identification
Working pressure is not one number for the family. It varies with material and size: brass 1/8 about 350 bar, brass 1/4 about 280 bar, stainless 1/8 about 450 bar, stainless 1/4 about 400 bar, and zinc-plated carbon steel about 420 bar. Design burst-to-working ratio is 4:1. To identify a fitting in the field, count threads per inch, measure the major diameter with calipers, and check whether the thread tapers along its length. BSP does not interchange with NPT or metric threads even when the sizes look close, so confirm the form before ordering. Send your measurements through our quote request form and we will match the thread.
Frequently Asked Questions
What does BSP mean on a grease fitting?
British Standard Pipe thread with a 55 degree Whitworth form.
What is the difference between BSPT and BSPP?
Tapered seals on thread flanks; parallel seals on a face O-ring or washer.
Which sizes are common?
1/8, 1/4, 3/8 and 1/2 inch; 1/4 and 3/8 are the most used.
Is the nominal size the actual diameter?
No; 3/8 thread measures about 16.66 mm across.
Can BSP replace NPT fittings?
No; thread forms and angles differ, they jam or leak.
How do I identify a BSP fitting?
Count threads per inch, measure diameter, check for taper.
Which material should I pick?
Brass general duty, stainless 316 wet or chemical sites, plated steel general industrial.
What pressure do they hold?
Roughly 280 to 450 bar working by size and material.
When is a 90 degree head used?
When the gun cannot approach a straight head straight-on.
Who supplies these fittings?
IsoHiTech Lubrication Systems, founded in 2023, engineering since 2006, builds and supports every unit. Email inquiry@isohitech.com for specifications and a quotation.
For sizes, materials or a quote request, contact our team.
