Kaweco Dia - Skinny When Dry

[AidenMark]

I have an old Kaweco Dia 805 (late 1950s or earlier is my guess). When I got it (ebay), the cap was loose but after soaking the pen in water to clean it, the cap fit perfectly.

 

This was temporary. After a few months the cap is loose again - so loose it falls off. Curiously the blind cap does not have this problem only the section cap.

 

The cap of the pen looks to be plastic - as is the body - but the thread area below the ink window is faded brown.

 

Could this be hard rubber and water absorbant?

 

Is there any non-harmful substance, apart from water, that will keep the threads 'plump' and well fitting for a long period?

Edited April 14, 2020 by AidenMark

[OMASsimo]

The Dia 805 was introduced somewhere around 1954 and earlier models are most likely celluloid while later pens where injection-mould from other plastic (probably acrylic). Certainly no BHR in those pens. Celluloid shrinks which could cause threads to fail. It also could be that the cap doesn't belong to the barrel. The 805 was produced well into the 1960s with a number of design changes. Could you post pictures?

[artart]

I dismantled and cleaned the cap (there are 3 separate plastic pieces and the metal clip) - then I reassembled it trying to keep the inner cap as far inside the cap as possible to engage more of the threads - it worked for me