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[Scalyback]

ok, yes I get that, so 1/4 inch bigger. grease nipples have a pipe in them for grease to run through, well, a drilling anyway.

In other news, the trafficators should be at the farmhouse today or tomorrow!

[Presto]

BSP (Gas) Thread Sizes. Quoted sizes for BSP = OD – ¼ inch. So we have ⅛ GAS = 28tpi x 0.383 ins [3/8 approx]; ¼ GAS = 19tpi x 0.518 ins [1/2 approx]; ⅜ GAS = 19tpi x 0.656 ins [21/32 or 5/8 approx].

[jefrs]

BSP are plumbing (water, not often gas 'cos it leaks) and work on the plumbing pipe size, which is nominal and requires clearance. As far as I'm aware grease nipples are not plumbing, they have a hole but don't need the extra surrounding metal for compression olive fittings. I'm not a plumber and more familiar with NPT and high integrity pipe fittings like Swagelok.



I just happen have a copy of ye olde engineer's workshop bible for drilling and tapping, the Zeus Precision "Data Charts and Reference Tables For Drawing Office Toolroom & Workshop" Metric Revision 1978/79 80p from Buck & Hickman Ltd.



I do not think you have BSP but BSF. If you have a tapered thread on the nipple it will interference fit into the parallel hole, if it is parallel you just screw it in. You may want to run some known-thread screws into the hole to gauge it. Near-enough may be good-enough or you may want to run a bottoming tap down it.

[Presto]

Just for the fun of it - Gas nut sizes (BSP) related to the internal diameter of 'old style' gas pipe. More recent pipe has thinner walls and so the sizing now relates to nothing in current use!

[Revband]

May as well give up now Presto, we both know bsp is also a gas fitting, but you can't win.

[Scalyback]

Could somebody with a Redditch centre stand please undo one of the nipples and see what it is? I now lean towards 1/4 BSF



With all due respect to the knowledge of Presto and Jefrs, I an going to hope they don't notice as I creep quietly out of the room, whilst they gas their pipes to death.

[Dennis C]

Hi Scalyback,

Just measured and it is 1/4" X 26 tpi with a tapered thread, measured with a calliper and thread gauge, the internal thread is straight, only the nipple is tapered (ooer misses) so it is most likely 1/4 BSCy. the taper is of course to give a tight grease-tight fit.

[jefrs]

Revband, Presto - I'm not making a point, no score, just providing information. We weren't allowed to use ordinary plumbing fittings on any gas pipes in the labs, going back over forty years that is. Interference taper BSPT was used for screw together iron gas pipes but not the smaller compression joints, if your Corgi fitter finds those on your gas boiler he'll have a fit.

We went metric during the sixties and that period was a right old mishmash of different screw sizes in use, especially as it followed on from the 'unification' (UNC/UNF) of british (BSW/BSF) and american threads (ANC/ANF). So if you can name it, you might find it on your bike. ISO-metric is its own kettle of worms.

[Dennis C]

Just thought I should clarify why I said BSCy rather than BSF, in the 50s and 60s most motorbike frame fittings were cycle thread, OK I know that they are almost identical but they should not be interchanged as they are 55 and 60 degree thread profiles.

[Presto]

No problem jefrs! It wasn't in my mind that my comment was a 'reply' to anything you'd said - just another comment. Your info is always interesting - and shows a depth of knowledge.