Please click on the picture below that most resembles your mixer.

Domestic tilt head model Professional bowl lift model
KitchenAid Artisan Tilt Head mixer with head tilted back KitchenAid professional bowl-lift mixer with bowl removed

Tracing their roots back to 1938 these models are designed for use in the home. They have a similar shape to the professional model and are similar in power. The tilting head allows the mixer to be short which allows it to stay on most worktops and fit under wall cabinets. There are more colours availableon these models compared to the professional version. These mixers are usually refered to as 4.5qt (US quart) models. Later models (KSM150 and KSM156 often called Artisan) have a taller 5qt bowl but still use the same whisks, beaters and dough hooks as the other tilt head models. The following model numbers are some of the common tilt head versions:K45SS, K45, KSM90, KSM150 and Artisan.  The model number often have their colour number and revision, i.e. 5KSM150BER3 is a 5KSM150 with British Plug (E would be European) and ER = Empire Red 3 = revision. 

Normally white, the professional model is found in many pubs and restaurants.  The main difference between this model and the domestic versions is the way the bowl lifts to the head.  As the head and the base are firmly bolted together it has less lateral movement when kneading dough.  The base is also easier to wipe clean.  The pedistal shares casting molds with the Hobart N-50.  On some bowl lift models various safety and overload switches are fitted.  The following model numbers are some of the popular bowl lift versions available: K5, K5SS (often read as K555 and KSSS), KPM5, KPM50, KSM5, and KSM50.  Some European models are prefixed with a 5, i.e. 5K5SS, 5PKM5, 5KPM50.