Needle Size for B12 Injection: 5 Must Know Tips Needle gauge and colour coding help in quick identification during injections and IV procedures. Understanding gauge size is essential for safe practice and nursing exams. Disclaimer For educational purposes only. Not medical Self injecting vitamin B12. Quick and painless jabs after a B12 by Dr Caroline Palmer Medium Amazon.com : 12 Gauge Veterinary Needles, Cattle Needle Poultry Injection Needles 10 Sticks, Suitable for Pigeons, Chickens, Ducks, Geese, Pigs, Sheep, Horses, And Other Large And Small Animals (12*20mm) : Patio, Lawn & Garden Needle Size for B12 Injection: 5 Must Know Tips