2.4mm Pipework expansion sections.  These are often seen at regular intervals on oil fields and allow for the pipes to flex with heat expansion.  
Pack of 6.  3 sections with increasing radius.  2 of each size.  
These are designed to fit with our 2.4mm diameter pipes. 
UNPAINTED
OO Gauge 1/76 scale but suitable for HO 1/87 scale as well.
Designed and manufactured by Goodwood Scenics Ltd in the UK