Webbing is available in multiple widths and numbers of what, which determine its strength?

The strength of webbing is primarily determined by the number of plies. Ply refers to the layers of material that are stacked together to form the webbing. Each additional ply in the construction of the webbing increases its overall strength and load-bearing capacity. This means that a webbing with multiple plies can handle heavier loads compared to a single-ply webbing of the same width.

Other factors, such as the material used and the width of the webbing, also play a role in its strength, but the concept of ply is specifically related to how many layers are used in its construction. Therefore, identifying the number of plies is key to understanding the load capacity of a particular piece of webbing in rigging and hoisting applications, making the choice of "ply" the correct answer.