# Opening Rules

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Your guard (guardrail) must block certain sphere sizes through any opening:

**Railing Infill**\
The space between posts (such as cables, rods, or panels) must block a 4-inch diameter sphere.

**Stair Guard Infill**\
The space between posts on a stair guard (like a railing) must block a 4 3/8-inch sphere.

**Stair triangle**\
The triangular gap formed by the tread, riser, and bottom element must block a 6-inch sphere.

**Why Viewrail uses 3-1/8″ cable spacing (on center)**\
With correct tensioning, 3-1/8″ spacing helps ensure deflection does not allow a 4″ sphere to pass through.
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