# Cheap UHV feedthroughs

**URL:** <http://forum.0xdbfb7.com/t/cheap-uhv-feedthroughs/164>\
**Category:** Materials & methods\
**Created:** [July 17, 2023, 9:04pm UTC](http://forum.0xdbfb7.com/t/cheap-uhv-feedthroughs/164 "2023-07-17T21:04:37Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![0xDBFB7](http://forum.0xdbfb7.com/user_avatar/forum.0xdbfb7.com/0xdbfb7/32/7_2.png) [@0xDBFB7](http://forum.0xdbfb7.com/u/0xDBFB7)\
**Post date:** [July 17, 2023, 9:04pm UTC](http://forum.0xdbfb7.com/t/cheap-uhv-feedthroughs/164/1 "2023-07-17T21:04:37Z")

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Purchased some NGK D8EA non-resistor gasket copper-core plugs. They’re pretty cheap at $5 to $10 apiece and very readily available. These have an M12 x 1.25 thread and a 3/4" (19 mm) reach, gasket seat, apparently equivalent to Autolite AR4152, NGK D8EA/2120, or Denso X27EP-U9.

Some spark plugs apparently use a talcum powder ring for sealing, which I can’t imagine is satisfactory at UHV; but I believe these style use a proper ceramic-to-metal seal.

Ben Krasnow has used spark plugs as well [for his SEM](https://www.youtube.com/watch?v=VdjYVF4a6iU), although interestingly he’s flipped them around, with the ceramic on the _inside_. This might help to prevent virtual leaks around the threads.

also similar to [https://gigabecquerel.wordpress.com/2019/06/02/quick-n-dirty-vacuum-feedthrough/](https://gigabecquerel.wordpress.com/2019/06/02/quick-n-dirty-vacuum-feedthrough/)

Ordered in some copper crush washers (#97725A250, M12 Screw Size, 12.2 mm ID, 15.9 mm OD, 1.3-1.7 mm thick) from McMaster. These seemed to seal up very nicely. A large amount of torque was required to seat them, and I’m not sure how the aluminum threads are holding up.

I only tested this down to about 2e-5 Torr (2e-3 Pa), probably because the chamber overall was leaky as a sieve.

 ![Screenshot from 2023-07-17 15-01-51](http://forum.0xdbfb7.com/uploads/default/original/1X/d64492ed5458e9833ff85bfc3956f096eadad37e.png)  
 ![Screenshot from 2023-07-17 15-11-37](http://forum.0xdbfb7.com/uploads/default/original/1X/9fde5b947f71fc75592f80dd8efb5f322725dcca.png)  
 ![Screenshot from 2023-07-17 15-13-13](http://forum.0xdbfb7.com/uploads/default/original/1X/f7eedae0e17539ad46f0a08bbdc0b1cd15c29200.jpeg)

In any case, the plug body is typically made of a nickel steel alloy.

Glass tubing for spark plug HV insulation;

[http://home.earthlink.net/~jimlux/hv/sparkplug.htm](http://home.earthlink.net/~jimlux/hv/sparkplug.htm)

[https://www.gsparkplug.com/shop/spark-plug-construction/](https://www.gsparkplug.com/shop/spark-plug-construction/)

I cut the existing gaskets off. The vacuum baseplate was about a quarter inch thick. I threaded these with an M12 x 1.25 tap (off Amazon, I think).

I’ve managed to put 45 amps through these plugs for short periods - worked great.

Solder wets the tip of these plugs very well if the surface is sanded slightly. broke the tip off

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<div class="post-metadata">

**Author:** ![0xDBFB7](http://forum.0xdbfb7.com/user_avatar/forum.0xdbfb7.com/0xdbfb7/32/7_2.png) [@0xDBFB7](http://forum.0xdbfb7.com/u/0xDBFB7)\
**Post date:** [June 8, 2026, 3:31am UTC](http://forum.0xdbfb7.com/t/cheap-uhv-feedthroughs/164/2 "2026-06-08T03:31:31Z")

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LRM: Suggets **J99 style** spark plugs.

“Industrial heater” / burner spark plug seems to be the search term.