What characteristic defines a scarf joint?

A scarf joint is characterized by its sloped surfaces that allow for a larger bonding area between the two pieces of material being joined. The specific slope of 1:10 or 1:12 enhances the joint's strength by distributing the load more evenly along the joint and reducing the likelihood of fracture. This configuration is particularly beneficial in applications where maximum strength is required, such as in aircraft structures where materials must withstand various stress factors during flight.

The other characteristics listed do not accurately describe a scarf joint. The cut being square with no angle would not allow for the increased surface area that the slope provides. Similarly, while adding a radius at the ends can improve the durability of certain joints, it is not a defining feature of a scarf joint. Lastly, the use of glue only, without any mechanical fasteners, does not establish a scarf joint, as many scarf joints can incorporate mechanical fasteners for enhanced strength and stability.