How do I create a regular expression of minimum 8, maximum 16, alphabetic, numbers and NO space?

^[a-zA-Z0-9]{8,16}$

You can specify the minimum/maximum gathered using {X,Y} as the boundaries.

Other examples:
^[a-zA-Z0-9]{8,}$ #8 or more characters
^[a-zA-Z0-9]{,16}$ #Less than or equal to 16 characters
^[a-zA-Z0-9]{8}$ #Exactly 8 characters

Regex cheatsheet

You just need to put bounds on, not the + (one or more) operator.

^[a-zA-Z0-9]{8,16}$

^[A-Za-z0-9]{8,16}$

Specify a min/max length for a part of an expression using {x,y}, where x is the minimum and y is the maximum.