Fixed versus detachable needles: the trade-offs — does this still hold?

Fixed versus detachable needles: the trade-offs — does this still hold? I have a specific reason for asking rather than idle curiosity, and the context is below.

Working notes on Fixed versus detachable needles rather than a conclusion. I would rather post the reasoning while it can still be corrected than post the answer once I am committed to it.

Everything below is checkable. Where I have taken a figure from somewhere else I have said where; where I have estimated, I have said that too.

Coring the stopper is a real phenomenon with repeated entries at the same point and blunt needles. Varying the entry point slightly and using a fresh needle prevents it.

Answering the question the opening post raises rather than the one it answers.

Filter needles are for drawing from glass ampoules where particulate is a real risk. For a stoppered vial they add dead volume in exchange for very little.

That is all I can say without guessing.

The arithmetic in the opening post is right; the assumption feeding it is the part to check.

Safety-engineered needles are worth using if you have children or anyone else in the house, and the retraction mechanism occupies dead volume that ordinary syringes do not.

I would rather say I do not know than round it up to an answer.

Needle length for subcutaneous delivery is a question about tissue depth and injection angle together. Short needles at ninety degrees and longer ones at an angle reach comparable depths.

A detachable luer needle plus hub can retain enough volume to matter. Whether it matters to you depends on your dose, and the arithmetic is worth doing once.

Nothing above should be read as advice about what anyone else should do.

Second this, and I would have said it less carefully.

Fixed versus detachable needles: insulin syringes usually have fixed needles (no dead volume loss to the hub). Luer-lock syringes use detachable needles (more dead volume). Fixed needles are preferred for small doses.

The reasoning is more useful than the number, which is why I have shown it.

Marking my place. If it changes for me I will come back and say so.

Building on post #9 rather than restating it.

Gauge is the outside diameter and higher numbers are thinner. Thinner needles hurt less and draw more slowly, which is the entire trade.

Syringe barrel size: common sizes are 0.3 mL, 0.5 mL, and 1.0 mL. Smaller barrels are more legible for small doses. Larger barrels hold larger volumes. Choose based on your dose.

If it helps: the failure mode here is usually boring rather than dramatic.

Dead volume: residual liquid in the hub and needle after withdrawal. Typical residual is 0.01 to 0.02 mL for an insulin syringe with a fixed needle. Accounting for it matters if precision matters.

It is the sort of thing that seems obvious in retrospect and was not at the time.