2 1/4 - 2-3/4 inch

-3AN x 1/8"NPT Short suit 2" wide rails (pair)

Through-frame fittings are used to pass brake lines, fuel lines, or other tubing cleanly and safely through a frame or chassis. The specific size and material, SS (stainless steel) and 1.5–2", indicate a sturdy, corrosion-resistant fitting for frames with a wall thickness between 1.5 and 2 inches. You can find these at automotive and hot rod parts suppliers.