Assign font custom font weights

Hi guys,

I followed this excellent post which helped me use custom fonts on my site - Adding Custom Fonts. However the post doesn't appear to explain how to assign a particular weight to a given style. 

So I guess I'd be looking for something like 

H2 {
font-family: 'Gotham'!important ;
font-weight: 'medium'!important ;
}

however the above doesn't seem to do anything.

Even better than this would be the ability to assign my custom font weights to Squarespace's numbered font weight system

e.g. 

100  =  thin

300 = x-light

400 = light

500 = book

600 = medium

700 = bold

800  =  black

900 = ultra

Any ideas?

Here's my site link -

My Site

password: thefalcon

Have you solved this yet?