Some splints are very simple, while others are very complex. Here are some examples.
Hand-based thumb spica
Uses: Skier's thumb, osteo-arthritis of CMC joint of thumb
Uses: carpal tunnel syndrome, wrist tendinitis
Forearm-based thumb spica
Uses: DeQuervain's tenosynvotis, scaphoid fracture
Uses: for wrist conditions where it is unnecessary to immobilise the wrist, but more to limit end-range of wrist movement
Functional resting splint
Uses: arthritis, tendinitis, stroke
Radial nerve palsy splint
Uses: Radial nerve injury to allow functional grasp and release
Flexor tendon repair splint
This would be specifically recommended by the hand surgeon who had repaired the flexor tendon in the palm or finger
Silver ring splints
Uses: Finger deformities e.g. arthritis - I take measurements for these, order them for you, and then fit them upon arrival.