Why Your 7/8 BSP Connector Won’t Fit That Large Garden Tap (and What to Use Instead)
You’ve bought a 7/8 BSP connector for your big outdoor tap – the one's people call farmers taps – and it looks the right size. It starts to screw on for a turn or two… then locks solid.
Forcing it only damages the threads.
This is a common problem with large UK garden taps.
The 7/8 BSP Problem
Most farmers taps use a 7/8 BSP parallel thread. That’s why the popular RoBox 7/8 BSP connector works for the majority of them.
But some of these large taps are actually made with an M30 metric thread instead.
M30 is almost identical in diameter (about 30 mm), so the connector feels like it should fit. The difference is the thread pitch – M30 has a finer thread. That’s why the 7/8 BSP connector starts to engage and then binds.
If this is happening to you, the 7/8 BSP product is simply the wrong thread. You need the matching M30 connector.
The Simple Fix
Stop forcing the 7/8 BSP connector.
Switch to the dedicated M30 version made by RoBox Design:
https://www.roboxdesign.co.uk/garden-tap-connector-m30
This is the correct thread for those taps that look the same size but refuse to take a 7/8 BSP fitting.
How to Check Quickly
- Clean the tap outlet.
- Try the 7/8 BSP connector by hand only.
- Screws on smoothly all the way → stick with the 7/8 BSP.
- Starts to turn then binds → you need the M30.
Never use pliers or a wrench to force it. Binding is the clear sign the pitch is wrong.
Why This Happens on UK Garden Taps
UK outdoor taps normally use BSP parallel threads (the British Standard Pipe straight thread). The common sizes are ½" and ¾". Larger farmers taps often use the less common 7/8" BSP size.
A few manufacturers use the metric M30 thread instead. Because the outside diameter is so close, the two threads look and feel almost the same until you try to screw them together.
That’s why a 7/8 BSP connector can appear correct in every way – until it locks after a couple of turns.
This issue is just down to the different thread profile and pitch. M30 is finer than the 7/8 14TPI thread form.
| Feature | 7/8 BSP (G7/8) | M30 × 1.5 |
|---|---|---|
| Thread Type | British Standard Pipe Parallel | Metric (fine pitch) |
| Outside Diameter | 30.2 mm | 30.0 mm |
| Pitch | 1.814 mm | 1.5 mm |
| Threads per Inch | 14 TPI | Approx. 17 TPI |
| Best Connector to Use | 7/8 BSP Connector | M30 Connector |
Summary for DIY Homeowners
- If the 7/8 BSP connector binds after starting to screw on, it is almost certainly an M30 tap.
- Use the M30 connector instead: https://www.roboxdesign.co.uk/garden-tap-connector-m30
- The standard 7/8 BSP version still works for the majority of farmers taps: https://www.roboxdesign.co.uk/garden-tap-connector-78
Get the right thread and your large outdoor tap will finally take a normal hose connector without any forcing or damage.