I have a service with a distribution panel carrying a s/p 20 amp breaker powering a camera pole with an in line disconnect. What size fuse required ?

Circuits are designed on the premise of what ampacity you need.
Do you know what size wire you have? The breaker size is determined by that to protect the circuit.

I have a service with a distribution panel carrying a s/p 20 amp breaker powering a camera pole with an in line disconnect. What size fuse required ?Explain this better. What is an inline disconnect, and where is it? I assume it is fusible which is why you are asking?