The American Society of Mechanical Engineers (ASME) publication B56.1-2004 (and previous ANSI versions), Safety Standard for Low Lift and High Lift Trucks, addresses modifications to trucks and the use of spinner knobs.

Paragraph 4.2.1 requires modifications which may affect the safe operation of the truck be approved in writing by the truck manufacturer.

Paragraph 4.2.8 requires a spinner **** to be used with steering mechanisms that prevent road reactions to cause the steering wheel to spin where one handed operation is required and gives technical installation specifications.

Paragraph 4.2.9 allows the optional use of a spinner **** with steering mechanisms that prevent road reactions to cause the steering wheel to spin and gives technical installation specifications.

Similar paragraphs will likely be found in the Canadian Standards Association (CSA) publication CAN-B335-04, Safety Standard for Lift Trucks. People in other countries should consult their national engineering standard organization such as BSI, SAA, SNZ, etc. for similar publications.

With the exceptions of stand up operated forklifts designed for one hand operation and the accommodation of a counterbalanced truck for a disabled person, I can't think of a good reason for the use of a spinner ****. Controls for lift, tilt, side-shift, and automatic fork positioning, etc. should not be operated while the truck is in motion. Activities such as eating, drinking, using a radio, using a cell phone, etc. should also be prohibited while the truck is in motion. Both operator's hands, excluding the above exceptions, should be on the steering wheel while in motion.

Due to the poor lateral stability of forklifts (especially when not carrying a load), I would not recommend spinner knobs for normal use. I see spinner knobs as a prelude to a lateral overturn.