Use this replacement 3/8 pen tube if you have damaged the pen tubes that came with your pen kit.
These pen tubes are 10" (approx 25cm) long come in a pack of 8 .They should be cut to the correct length using a fine saw.
Please note, the tube fits a 8mm drilled hole. The tube diameter is a bit smaller than 3/8 to fit the drilled hole and have space for a glue layer.
After cutting, they should be squared using a barrel trimming set.