Fastener Edge Distance: How Close Can a Hole Be?

Fastener edge distance is the amount of material between a hole and the nearest edge of a part, and it decides whether a loaded joint tears out.

How Much Metal Should Be Left Between a Hole and the Edge of a Part?

A common starting point is about twice the fastener diameter (2D) from the hole center to the edge, with 1.5D used as a minimum in some cases. The right number depends on the load, the material and how the part is made.

An r/MechanicalEngineering user asked how much metal to leave between a hole or thread and the edge of a part. An aerospace stress engineer replied that you generally want 2D from the edge to the hole center, and can go down to 1.5D for non-critical attachments. Another reply said 2D is the target and 1.5D is possible with test data for the material. A third pointed to the tables in Machinery's Handbook, warning that many of those minimums are for manufacturing, not for loading. These are rules of thumb, not a standard.

What NASA's fastener standard says

NASA-STD-5020B, approved in 2021, has an appendix on showing a fastener has a low likelihood of fatigue failure by similarity to a known design. One of its conditions is that the minimum edge distance, measured from the hole center to the closest edge of any clamped part other than washers, is at least 1.5 times the bolt diameter. That's a condition inside one analysis method, not a universal rule. The same document notes that thin-wall inserts suit joints that need less edge distance, while key-locked inserts need more to prevent shear tear-out.

What changes the answer

• Load direction. A load that pushes the fastener toward the edge is the one that tears it out.
• Material. The 1.5D allowance above came with test data for the material, so don't carry a number from one alloy to another without checking.
• Tapped holes. Wall left beside a thread is set by the thread's major diameter, not the tap drill size.
• Process. In sheet metal, holes near bends and edges have their own rules. See how close a hole can be to a bend line and PEM hole-to-edge distance.

Fastener edge distance: practical tips

• Start at 2D and justify anything tighter.
• Check that the washer or bolt head doesn't hang over the edge.
• For loaded joints, do the bolted-joint analysis instead of relying on a rule of thumb.
• If the hole position itself is tight, see how tight a tapped hole position tolerance needs to be.

At DigiForge

Our CNC service covers 3-, 4- and 5-axis milling and turning, and every quote is reviewed by an engineer before it goes into production. Edge distance is still your design decision. If a hole sits close to an edge and you want a second look, ask us when you quote.