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GuideSizing

Frame size vs clear opening

This is one of the most common sources of ordering mistakes. Buyers often quote only the frame size or only the visible top size, while the real maintenance need depends on the clear opening inside the frame.

What is frame size?

Frame size is the overall outer footprint of the frame assembly. It tells you how much surface area the product needs to sit properly on the chamber or slab top.

What is clear opening?

Clear opening is the usable inside access opening for workers, tools, cables, or inspection work. It determines whether the chamber is actually serviceable after installation.

Check itemWhy it mattersWhat to ask before ordering
Clear openingControls maintenance access and usable internal opening.How much free opening do workers, tools, or cables need?
Frame sizeControls outer seating and support on the slab or chamber top.Will the chamber top provide enough bearing area for the frame?
Thickness or heightAffects seating depth, durability, and final finished level.What cover depth is needed for site conditions and support detail?

Simple selection process

  1. Measure the chamber opening or access requirement.
  2. Choose the required clear opening first.
  3. Confirm the matching frame size can sit properly on site.
  4. Check load class and application requirement.
  5. Review the exact product variant page before placing the order.

Typical mistakes to avoid

  • • Treating the frame size and clear opening as the same thing
  • • Matching top slab size but not maintenance access
  • • Comparing two products only by overall dimensions
  • • Ignoring clear opening when selecting telecom or inspection chambers