[KensRedZed]

Hi Pip,

Evergreen styrene round tubing is available at most hobby shops.

https://evergreenscalemodels.com/collect...rene-tubes

Numbers 225 (for 2-56 inserts) and 227 (for 4-40 size inserts) are two common sizes.

Brass inserts can be found at places like Professor Motor.

https://www.professormotor.com/product-p/pmtr7012.htm

You will need to do your own homework to make sure the inserts you buy fits the inside of tubing. I don't know what the Professor Motor inserts above fit.

I buy inserts from a bulk supplier that only sells them by the box.

Best of luck with your builds!
Ken