Hillside Washers are used when connecting braces that pass through structural members at any angle other than 90°. Unlike inside connections requiring Clevis Rod Assemblies (Fig.1), when the brace passes through the structural member it eliminates the need for Clevises and Clevis Pins.
Fig. 1 
As shown in Fig. 1 a Clevis Plate welded to the I-beam acts as the anchor to secure the clevis.
Fig. 2 shows the same Turnbuckle Rod Assembly but in this case the design allows a hole to be drilled or punched in the steel member and the rod to pass through. If the rod approached the steel member at a 90° angle a simple washer and nut on the outside would be sufficient. This will not often be the case. The purpose of the Turnbuckle Rod is usually as a sway brace. As such it only functions at an angle, and requires an opposite sway brace to be effective. (Fig. 3)
Fig. 2
While the angle is require for the rod to function it presents a second anchoring problem. The washer and nut require a solid and perpendicular surface to seat properly and provide the desired strength without deflection.
This can be accomplished with a bevel washer or specially fabricated angled plate, but both of those idea have difficulties, and also require predicting the exact angle prior to erection. This is not difficult, but is another variable that may create a problem.
The easiest, fastest and least expensive way to anchor a pass through angle connect is with a Hillside Washer. (Shown in Fig. 2) The flat bottom sits firmly on the steel surface. Its half-moon shape allows it to present a perpendicular surface to the rod regardless of what angle it comes in at.
Fig 3.
Of particular importance is the Hillside Washer has a tab that slots into the hole in the steel I-Beam. This tab locks it in place so that when the assembly is tightened the Hillside Washer does not slide in the direction of the tension. This would cause the Turnbuckle Rod to contort
Note, when a pass through rod is used Clevises are not. There may be a Turnbuckle but it is not required. All the necessary take-up can be achieved by tightening the nut at the Hillside Washer. If all threaded rod is used the take-up is unlimited. If round bar is used take steps to assure there will be adequate threading for the necessary take-up.
