The starting question
Which dimensions increase the gap, which reduce it, and what range does the assembly actually need?
For your own project
Which part do you need help with?
Start with what you know. Keep the undecided details open for discussion.
You bring
The parts, photos or measurements you already have.
We can help explore
How the pieces connect, move and leave room for access.
Discuss next
Which interfaces must stay fixed, and what can change?
Describe the relationship first
Identify the two surfaces or features that define the gap. State whether you need clearance, contact or an intended interference. Record the operating condition and what the assembly must do; the calculator does not choose the acceptable range.
Follow one dimensional path between those features. Give every dimension a name, units, nominal size, tolerance and a direction. A dimension that increases the gap is positive; one that reduces it is negative.
Use a full-range example
An opening of 30.00 ±0.10 mm minus an insert of 29.80 ±0.05 mm has a nominal gap of 0.20 mm. The smallest gap is 29.90 −29.85 =0.05 mm; the largest is 30.10 −29.75 =0.35 mm. This is the full range permitted by those size limits.
The ±0.15 mm worst-case variation adds the two tolerance contributions even though the insert dimension is subtracted. Negative direction changes the nominal sum, not the sign of the uncertainty contribution.
Know what the model leaves out
A one-dimensional size chain does not include angular misalignment, geometric tolerances, contact deformation, temperature or coating growth. Identify the relevant effects with the responsible designer before making an acceptance decision.
RSS is a statistical model rather than a guaranteed boundary on all allowed sizes. Independence and the interpretation of the input distributions matter. Our customer tool displays worst-case bounds without assigning a fit class, confidence level or manufacturing approval.
Bring this to the review
Your working checklist
Use these prompts to record open questions. Checking a box does not approve a design or manufacturing process. Selections last for this page visit.
References & further reading
References support the named topic; they do not certify a design, setup or product.
Planning guidance and illustrative examples. Confirm project-specific requirements with the responsible design, manufacturing and quality teams.
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