Boeing 737-800 variants

[Spoilermixer]

Hello,
can anyone explain to me the exact meaning of the last two digits on Boeing models like for example:
B737-8AS
B737-86N
B737-8Q8

i understand its a variant but what exactely can i know just by looking at these digits?

Thank you,

Spoilermixer.

[mbcxharm]

Boeing customer codes:

http://www.airlinecodes.co.uk/boeing.asp

[Spoilermixer]

Thank you mbcxharm,
very helpful.

Cheers,

Spoilermixer.