Also used for smoking especially speed or heroin/opium.
A folded piece or strip of foil held with one hand and lit with the other.
The pen tube is then held by the lips and used to extend to the foil and the smoke coming from it.
Can be for snorting too, however the rush is not as big as with smoking it.
Most that snort also eventually smoke, but the pen tube can lose alot to sticking.
Regular drinking straws are preferred for snorting, because they can be split to get what sticks inside.
The preferred straw of choice for snorting?
MacDonalds!
Larger diameter and non-sticky!
And it just seems you can never find the last pen tube when you need it again.
Thats why so many collect.
Plus you lose the other pen parts when your high.
Hope this helps.
Be Well