bianchi10

I have never been a handy guy so the last place you would find me at is a hardware store. Because of this, I am not familiar with the sizing of bolts. I'd like to order some titanium replacement bolts for my stem, seat post clamp...etc but not sure what size to order.

For example:

M5x16
M5x20
M6x16
M4x10

ETC...

I would imagine the second number is in regards to the length? Is there an easy way to tell which size bolts I will need besides taking them off and going to a hardware store and inserting them into their testing holes?

thanks