injection question

The smallest one I could find.

25-27 gauge

27 gauge.

Try 29, 30, or 31.

I think we, as a profession, use much larger needles than necessary. I give IMs in the deltoid on nonobese individuals using what my facility considers a SQ needle, 25g, 5/8inch. If the deltoid is well defined, under only a small amount of subcutaneous tissue, why would I reach for a 21g 1.5 inch? Sure, that might be appropriate for a leg/glute/obese patient, but otherwise it is just thoughtlessly cruel.

Edited to add: Incidentally, 25g for a SQ! And I have seen some nurses reach for 23's! I use TB needles for most of my SQ, and I would use it for the purpose you describe.

I always use an insulin needle for injecting heparin because it's given in 1ml amounts and the smaller needle causes less bruising.