How do I tell length of velvet shocks?

[eddscott]

Might sound like an odd one but I'm building a Optima Mid and want to use as many updated products as possible. This includes the velvet shocks.

However, I can't work out what size to get. I don't understand what is being referred to with the numbers - 46, 42, 38,

I've been looking on auctions sites waiting for a full SP set but no luck so far.