If a non injecting T2 may be so bold as to poke his nose in I did find the following while perusing the net.
My experience in the area of injections is manly in giving them or receiving them and have only rarely injected myself.
"
Based on my own experiences, as both
a person with diabetes and a nurse, I would
recommend the following as a starting point:
Longer needles for overweight and obese
adults (BMI >27kg/m2
) using a pinched
skinfold.
Medium-length needles for normal-weight
adults, children and adolescents using a
pinched skinfold.
Shorter needles for children and adolescents
(aged 0–18 years) with or without an elevated
skinfold, or adults without an elevated
skinfold.
Research published recently (Birkebaek et al,
2008), suggests that 4mm needles reduce the
risk of intramuscular injections, and can be used
without pinching a skinfold; however, there is
evidence that in lean young men there is still a
risk of an intramuscular injection when insulin
is given in the abdomen or thigh using a 5mm
needle without an elevated skinfold (Frid, 2006). "
https://www.diabetesonthenet.com/uploads/resources/dotn/_master/760/files/pdf/jdn12-10pg364.pdf