Just gonna chime in here, I use #20 to draw (been on TRT for awhile) and #22 or #23 to pin. #20 is good to draw from 10mL vials with the silicone 'self-healing' tops. Anything larger the hole is too big and ruins the vials tops quick..
Some say, why not #25, #27, thinner is better for injection... Well not really always plunger pressure is a BITCH when injecting oneself with thin #25-27 slim pins, even if you get pricier thin/clear oil gear. Which if you want high concentration + low-solvents is pricey.. for quality sake.
For good oils, I find the sweet spot to be #22, #23 for injection - small enough to not damage much - but EASY to push the plunger in. I don't want that needle digging / moving around... because my hand is shaking trying to exert to much force on the plunger while the off hand holds position steady, etc.
In other words, if I can make a clean injection + push plunger smooth + and remove without pushing a bunch or moving the needle around = less damage to the muscle I just pinned, less scar over time with #22 or #23 gauge..
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Now let's talk needle length for IM, seriously 1" is plenty, 1.5" I find to be too long _ usually extra shaft sticking out and I'm just holding the needle offhand. I mean I'm 6'2" and ~200lbs, how thick are people's skin/fat layers, seen some crazy long needles recommended for shoulders/glutes?