Tweeti use one inch 23 gauge. as far as the best spot is a couple inches above mid thigh. i stand up straight and let my arms fall by my side and my birdie finger falls out mid thigh. i hold that spot and grab my needle sit down and move my finger 2 to 3 inches above where my finger is and inject. i use to do right where my finger fell out and it would be hard to workout my legs because i couldn't bend my leg but, as soon as i moved the shot up a little i was good to go.