Just a word of advise, we have figured this out through trial and error, we have come across two types of needles
for the pen
. One is just the needle (it screws on to the top of the pen
) the other is a needle (it also screws on to the top of the pen) but it has a plastic cylinder around the needle which you need to press firmly against the skin in order for it to retract the plastic then exposed the needle. My son found this needle very uncomfortable.