Sealing plug for radiator control tee

If, like me, you've got this kind of heating radiator adjustment tee (see first and second photos), you'll probably have a leak the first time you try to adjust the return flow. And if you've lost the protection and sealing plug, you'll be in a lot of trouble.

I couldn't find any such stoppers for sale, so I had to make one by 3D printing.

Cap specifications (cap.stl file) :

• Even if the return temperature isn't normally very high, it's better to use a heat-resistant plug. For my part, I used ASA.

• The plug's outside diameter is 26mm. Its length is 24mm (2mm longer than the original).

The tapping has the following characteristics (Freecad labels):

• Unified fine thread (UTS)

• 0.40mm clearance

• Size 5/8

• Thread on 15mm (but in theory, 4mm is sufficient).

Can be fitted with an O-ring for sealing. But it's better to use filasse with jointing paste, as in practice, the O-ring only applies imperfectly to this type of tee.

I've also made a test version (file bouchon_test_filetage.stl) that's quick and easy to print out, so you can check that the threads match.

Version 2: compared to the version initially published, I've made a modification to the plug to improve its watertightness. I noticed a leak at the end where the thickness was 2mm. It's now 5mm thick, and so far I haven't noticed any leaks.

I also made a print with a wall thickness of 10mm, which in practice means 100% filling. But still, for reasons of watertightness, it's better to play with thickness rather than filling.

For printing, I use Cura's standard settings for ASA except :

• Activation of stretching on all layers to ensure good flatness of the part that receives the joint if you put one. This activation is unnecessary on the test version.

• Number of wall lines = 5 (important. I've had leaks with the standard value of 2). For the test version, you can settle for 2.

• And for ASA, no ventilation