various screwplug sizes

1.25″BSP, 1.75″BSP, 2″”BSP, 2.25″ SCREWPLUGS


Examples of some of the various screwplug sizes available, these are undrilled, therefore can be used as a blanking plate or for our customers who are unsure of their requirements, to screw into their socket before anything is manufactured bespoke. Very useful!

This is the simple 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

…and this is the complicated version,

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.

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″ TROMBONE 2 STAT
2″ TROMBONE 1 STAT
1.75″ TROMBONE 1 STAT
1.5″ 3 HAIRPINS 1 STAT
1.25″ 3 HAIRPINS NO 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 hairpin, we mean a U bent element, and trombone indicates double looped. 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.