All through bolts should have _____ at the bolt head and nut.

The correct answer is that all through bolts should have washers at the bolt head and nut. Washers play a critical role in the assembly of fasteners. They help distribute the load of the bolt and nut, providing a larger surface area to reduce localized stress on the materials being fastened. This is particularly important in preventing damage to fragile surfaces or when fastening materials that may deform under pressure.

Additionally, washers can help to prevent loosening of the nuts due to vibration and environmental conditions, improving the overall reliability and longevity of the connection. They serve as a barrier that can help protect the surfaces of the materials from abrasion and help to keep the bolt in place over time.

While other options like rings, nuts, and screws are related to fastener assemblies, they do not fulfill the specific purpose that washers do in ensuring stability and load distribution for through bolts, making washers the essential component in this context.