Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

Howdy Harry ..... and a great big WELCOME to the Forum!

Not any too sure where you might be able to find a proper sized Brass Pressure Gauge, but you likely will not need one that exceeds about 30 psi or 2 bar.

Wilesco sells a pressure gauge with adaptor that should probably fit your D405, though it isn't specifically listed it doesn't seem. Based on the listing it would seem likely that the threads in the bushing in the boiler would be M5.

See it here:

https://www.wilesco-shop.de/en/pressure-gauges/manometer-with-connection-on-the-botton-m6-30-mm-diameter-incl.-adapter-01529-thread-m6-m5-for-d18-d20-d22-d141-d430-t125.html

I should point out that Mini-Steam appears to sell the exact same unit, and may perhaps be easier for you to deal with, depending on where you are actually located.

See it here:

https://www.ministeam.com/product/Wilesco-Parts-01528/Toy-Steam-Engine-Parts

This British company may have something suitable in brass that would be small enough for you, though looks like an adaptor would be needed as well on the smallest 1/2" size. If you can live with a 3/4" dial, then it may be available with the correct thread.

See here:

https://www.miniaturepressuregauge.com/model-engineering/

Best of luck with your quest and let us know how you make out!!!