You can do it in several provided ways.
Create appropriate Class Structure for Part ItemType (go to Administration\ItemTypes, edit Part, use Class Structure field). Let two classes exist: Bolt and Motor. Then add required properties in Properties tab: Type, Diameter, etc. (assign /Part/Bolt for them in Class Path column); Horsepower, Power Supply, etc. (assign /Part/Motor for them in Class Path column). So, classes and class specific properties are configured. Now you need to display/edit them in appropriate way. Options:
1. Setup Show Parameters Tab=Always on Part ItemType form. Go to Design\Part, create a new instance, select Type=Bolt. Then Parameters tab is populated with appropriate properties. You can modify their values.
2. In Part ItemType, go to Views tab, create a new form, set Classification=/Part/Bolt in the grid. Edit the form and add corresponding class-specific fields to it. Then when you create a Part instance and select Type=Bolt, then this form will appear with the required properties populated.
3. You can write javascript code for standard Part form to display class-specific fields on Type field value change. The method mockup already exists on standard Part form classification (label is Type) field.