A crack stem is a glass tube that is used to smoke crack cocaine

Crack cocaine

Crack cocaine is the freebase form of cocaine that can be smoked. It may also be termed rock, hard, iron, cavvy, base, or just crack; it is the most addictive form of cocaine. Crack rocks offer a short but intense high to smokers...

 also known as freebase cocaine.

The glass tube stem in New York city is sold in "bodegas

Convenience store

A convenience store, corner store, corner shop, commonly called a bodega in Spanish-speaking areas of the United States, is a small store or shop in a built up area that stocks a range of everyday items such as groceries, toiletries, alcoholic and soft drinks, and may also offer money order and...

" or "corner stores". It is illegal to sell a stem with a metal filter in these stores but many sell them anyway. However a loophole

Loophole

A loophole is a weakness that allows a system to be circumvented.Loophole may also refer to:*Arrowslit, a slit in a castle wall*Loophole , a short science fiction story by Arthur C...

 in the law allows these stores to sell glass pens which when the ink is removed becomes a "rosebud" or glass tube (stem), with a plastic flower inside the tube. Although there is only one reason why they are sold (to smoke crack) there is no law being broken by selling a stem in this way. If a person is caught by the police with a glass tube that has no metal filter and no "crack cocaine" residue in the stem, that person cannot be arrested or fined for having illegal drug paraphernalia

Drug paraphernalia

Drug paraphernalia is a term used, often with a slightly negative connotation due to its use in criminal law field e.g. "possession of drug paraphernalia", to denote any equipment, product, or material that is modified for making, using, or concealing drugs, typically for recreational purposes...

on their person.