The Yamaha part number 91800-16016 (also shown as 91800-16016-00) corresponds to a Pin, Dowel.
This dowel pin is an original equipment manufacturer (OEM) part that has been superseded by a new part number, 99530-14016-00, which itself superseded several older numbers.
Models this part fits
As an engine alignment pin, it was used on a wide variety of Yamaha models over the years. Examples include:
ATVs: Grizzly and Raptor series, including the YFM250R and YFM350 (Big Bear).
Motorcycles: Various models, including the TDM series.
Other Applications: Yamaha also uses this type of dowel in other power equipment.