Explaining Needle Sizes

One of the constant battles I have in my work is getting people to understand why it’s so important to take the right gauge needle. Using bigger needles will speed up the amount of damage done to the vein and increase scaring. Increased scaring can rapidly lead to veins becoming unusable and even to developing DVT (Deep Vein Thrombosis).
But how can you get this point over?
People are very bad at understanding things they can’t see, not just drug users but all of us. That’s why we tend not to change our lifestyles until something major like a heart attack happens. Things happening in the body are just too …. abstract.
So we need some way of explaining the damage done in other ways, which is something I’ve been thinking about for a while now, here’s what I’ve come up with so far.
2 in 1

Paper
If you have some paper its possible to punch holes though this with each pin size, the paper can then be held up to the light so you can see the size of the hole that would be in the vein.
Another great (but more costly) way to do this would be to use a banana, as this will involve breaking the ‘skin’ on the banana it may make the result seem more real and identifiable to someone who injects.
We need to develop more imaginative ways of demonstrating the damage caused by these bigger needles,
I’d be really interested to see what other ways people are doing this, if you have a great idea please share this in the comments.

Update
Shortly after I wrote this article I was delivering some training and one of the candidates on that training decided to try for three in a pin, and managed it with not only two 30g needles but added in a 29g needle.
In my mind this really demonstrates the size of the hole you'd be making on the vein, the bigger the hole the shorter the life of the vein.
