Immersion Heater Screwplug Sizes

Immersion Heater Screwplug Sizes

There are a lot of screwplug sizes, as evidenced in Wikipedia article here, but generally speaking the industrial standard in the UK is 2.25″BSP, measuring 2.5″ across the threads, just to confuse matters, and the domestic standard is 1.5″, measuring a tickle under 1.9″. Folks who are unfortunate enough to have other sizes fitted are likely looking at a bespoke build & a coupla weeks wait.

  • BESPOKE Industrial Immersion Heaters.
  • Available at any kW loading from 500w up to 27kW.
  • 1″, 1.25″, 1.5″, 1.75″, 2″, 2.25″ and 2.5″ screwplug sizes are available in brass.
  • 2″ and 2.25″ BSP also available in stainless steel.
  • Available with 1 or 2 thermowells at 7, 11 or 18″ for thermostats / cutouts.
  • 1 additional M25 cable entry glands as an option.
  • Available with no thermowell if specified by the client. If you don’t need it, omit it from the build, as it is an unecessary weak point.

Call Jamie on 01827 215684 to discus your Immersion Heater Screwplug Sizes needs.

If you decide you prefer to go Over the Side of the vessel, have a look at our Vat Heaters Range.

Even more Useful Stuff.

various screwplug sizes

BSP really stands for British Standard Pipe, but some days it feels like it should stand for Bloody Sizeable Pain when it causes confusion. Best to be sure before ordering, as bespoke items cannot be returned!2.25″BSP is stock & standard for our Industrial purposes. 1.5″BSP is Domestic Standard in the UK, and we can do them bespoke, but our heaters are Industrial Quality, Fit & Forget, IP67 terminal box, highest quality elements manufactured in the UK using the highest quality component parts. So we simply don’t compete with the “Eastern” shite online for 3 shillings & sixpence.

Tables.

This is the simple INCH version…

BSP
“		 DIAMETER
ACROSS
THREAD
“
1/2 .825
5/8 .902
3/4 1.041
7/8 1.189
1 1.309
1 & 1/4 1.650
1 & 1/2 1.882
1 & 3/4 2.116
2 2.347
2 &1/4 2.537
2 & 1/2 2.95

…so 2.25″BSP measures 2.537″, great!Then my codged version, cos even I have to admit mm are a good deal easier to work with…

BSP” ⌀ ACROSS
THREAD”		 INTERNAL
BOSS mm		 EXTERNAL
SCREWPLUG mm		 Circumference
mm
0.25” 0.518 41
1/2 .825 66
5/8 .902 72
3/4 1.041 83
7/8 1.189 95
1 1.309 104
1 & 1/4 1.650 39.5 41.5 131
1 & 1/2 1.882 44.8 47.7 150
1 & 3/4 2.116 51.2 53.5 168
2 2.347 57.5 59.2 187.2
2 &1/4 2.537 62.5 65.4 206.4
2 & 1/2 2.95 72.4 74.9 236.2

…and this is the complicated version, from Wikipedia –

Thread Form Type Major Diameter mm d=D Pitch mm p Threads per inch tpi Pitch Diameter mm d2=D2 Minor Diameter Male Thd. d3 Thread Height H1 Tap Drill Diameter mm
1/8 “ BSPP/BSPF 9.728 0.907 28 9.147 8.566 0.581 8.7
1/4 “ BSPP/BSPF 13.157 1.337 19 12.301 11.445 0.856 11.6
3/8 “ BSPP/BSPF 16.662 1.337 19 15.806 14.95 0.856 15
1/2 “ BSPP/BSPF 20.955 1.814 14 19.793 18.631 1.162 19
5/8 “ BSPP/BSPF 22.911 1.814 14 21.749 20.587 1.162 20.75
3/4 “ BSPP/BSPF 26.441 1.814 14 25.279 24.117 1.162 24.5
7/8 “ BSPP/BSPF 30.201 1.814 14 29.039 27.877 1.162 28
1 “ BSPP/BSPF 33.249 2.309 11 31.77 30.291 1.479 30.5
1 1/8 “ BSPP/BSPF 37.897 2.309 11 36.418 34.939 1.479 35
1 1/4 “ BSPP/BSPF 41.91 2.309 11 40.431 38.952 1.479 39.5
1 3/8 “ BSPP/BSPF 44.323 2.309 11 42.844 41.365 1.479 41.5
1 1/2 “ BSPP/BSPF 47.803 2.309 11 46.324 44.845 1.479 45
1 3/4 “ BSPP/BSPF 53.746 2.309 11 52.267 50.788 1.479 51
2 “ BSPP/BSPF 59.614 2.309 11 58.135 56.656 1.479 57
2 1/4 “ BSPP/BSPF 65.71 2.309 11 64.231 62.752 1.479 63
2 1/2 “ BSPP/BSPF 75.184 2.309 11 73.705 72.226 1.479 72.5
2 3/4 “ BSPP/BSPF 81.534 2.309 11 80.055 78.576 1.479 79
3 “ BSPP/BSPF 87.884 2.309 11 86.405 84.926 1.479 85.5
3 1/4 “ BSPP/BSPF 93.98 2.309 11 92.501 91.022 1.479 91
3 1/2 “ BSPP/BSPF 100.33 2.309 11 98.351 97.372 1.479 97.75
3 3/4 “ BSPP/BSPF 106.68 2.309 11 105.201 103.722 1.479 104
4 “ BSPP/BSPF 113.03 2.309 11 111.55 110.072 1.479 110.5
4 1/2 “ BSPP/BSPF 125.73 2.309 11 124.251 122.772 1.479 123
5 “ BSPP/BSPF 138.43 2.309 11 136.951 135.472 1.479 136
5 1/2 “ BSPP/BSPF 151.13 2.309 11 149.651 148.172 1.479 148.5
6 “ BSPP/BSPF 163.83 2.309 11 162.351 160.872 1.479 161.5

I hope these are useful for reference purposes.

Limitations.

More importantly for us, on a daily basis, are the following limitations as to what will fit onto the smaller screwplug sizes. We deal with up to 2.25″ only, with 2.5″ being accommodated by fitting a brass adaptor to 2.25″ screwplug.

2.25″ 3 loops + 2 STAT
2″ 3 loops + 1 STAT
1.75″ 2 loops + 1 stat / 3 U + 2 stat
1.5″ 3 U 1 STAT
1.25″ 3 U NO STAT or 1 element looped  + 1 stat

Anything smaller than a 1.25″ screwplug will be limited to 1 element, having immediate implications for the achievable watts density.  Likewise, being limited to U bends only, makes reducing the watts density more problematic. Many domestic and commercial plumbing applications use 1.5″BSP, and are thus limited to 3 hairpins and only 1 stat pocket. maximising the immersed length of those U’s is all that can be done to reduce the watts density. To overcome the issue of only 1 stat pocket, we find ourselves increasingly selling dual control and cutout stats.By U bent element, we mean

…and looped means –

To determine what element is suitable, for U’s you merely double the maximum immersed length available, ie, 24″ immersed length will use U bent 48″ elements. However, if double looping is possible due to the screwplug size and other factors relating to the application (cleaning, etc), that 24″ maximum immersed length could be multiplied by up to 3.5, allowing the use of 84″ elements. See the watts density article to appreciate what a difference that will make. 48″ to 84″ almost double the hot element available, so is almost going to halve the watts density. A big issue on little screwplugs.If you wanna buy some stuff, take your pick betweenImmersion Heaters UK LtdBreweryHeaters.co.ukHeatingElements.co.uk…but tbh, all roads lead to Jamie, on 01827 215684.Thanks for visiting, please leave a comment.

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