Spinner knobs offer better steering control for individuals with arthritis or prosthetic devices. Modern tractors with power steering require little steering effort, but a variety of conditions can make gripping a normal steering wheel difficult. Control handles should be 1.5 to 2 inches in diameter. The knobs are reasonable in cost and average around $12. You can also buy knobs made especially for riding lawn mowers.
Also consider adding a plastic extension to the tractor or truck ignition key to help provide more gripping surface and reduce wrist strain.
In your local community:
Northern Tool & Equipment
Tractor Supply Company
Disclaimer: The vendors listed do not represent an endorsement by AgrAbility in Georgia and is provided only as an introduction to the many vendors that produce adapted products.