It is determined by the size of the veins
18-to 22
A small, thin needle called a butterfly needle or a catheter needle is commonly used for chemotherapy. These needles are designed to be gentle on veins and can accommodate the flow of chemotherapy drugs.
The best gauge for fragile veins would depend on many factors. The patient often already knows what gauge you should use. Most often that is a butterfly because they are the smallest available.
The medical professionals collecting the blood have a wide selection of needles of different gauges (or "bores") to cover all circumstances. They can start an IV on a newborn with the right gauge needle.
I wouldn't recommend it. 22 gauge is smaller than 18. The smaller the number, the larger the ring/needle. If you use an 18 gauge needle and then put a threaded 18 gauge ring in, you are likely to have more pain. I would use a 16 gauge needle and then put the 18 gauge ring. The threads won't tear the new flesh, and you're less likely to chicken out because it hurts. Remember to push the needle through with the jewelry, because if you take the needle out, you'll lose the hole before the jewelry goes through. But then again, you really ought to go to a professional.
a treatment modality whereby the doctor seals off the small blood vessels that cause spider veins by passing a weak electric current through a fine needle to the walls of the veins.
Yes, use the thinnest (highest #) gauge needle possible, 30+ gauge with a 3/8" tip most likely. Technique is everything, make sure to register on the first hit. The veins in your hands are fragile & if you mess them up it'll be obvious what's going on...
A popular gauge.
Not really. I have them as well and I am a very fit teenager.
Doing it slowly may help
Venules.