Final answer:
The 'Jam' is not a cap screw head but a type of nut, whereas 'Round', 'Fillister', and 'Hex socket' are all types of screw heads.
Step-by-step explanation:
The question asks to identify which option is not a type of cap screw head. Looking at the options provided:
- Jam
- Round
- Fillister
- Hex socket
The Jam is not actually a type of screw head but is rather a type of nut. Round, Fillister, and Hex socket are all common types of screw heads used in fastening applications. Round and fillister heads are somewhat similar in shape but are distinct from hex socket heads, which are designed to be driven by an allen wrench or hex key.