Media lodging risk calculator
Almost every media selection guide compares the media’s largest dimension to your hole. That is the wrong variable. What governs whether a piece passes through is its smallest silhouette across every orientation. That is why a one inch cylinder drops through a 5/16 inch hole.
Your part and media
Result
The one inch cylinder that fits a 5/16 hole
Take a ceramic cylinder 1/4 inch in diameter and 1 inch long. Its largest dimension is 1 inch. Every selection guide that compares largest dimension to hole size will tell you it cannot fit a 5/16 inch hole.
Stand it on end. The silhouette is a circle 1/4 inch across. It drops straight through without touching the sides. Length never mattered.
The reason is simple once stated: a rigid convex body passes through a hole in whichever orientation suits it, not the one that happens to be longest. So the quantity that governs is the minimum silhouette across all orientations, which we call Dpass. For a right cylinder that is the diameter. For a cone, the base diameter. For an equilateral triangular prism it is the smaller of 2s ÷ √3 and √(s²+t²). For a regular tetrahedron of edge a it is exactly a, via the square projection of side a ÷ √2.
What is exact here and what is not. The Dpass figures are exact closed-form geometry for idealised rigid shapes and you can check any of them by hand. Real media has rounded corners, dimensional scatter and wears out of shape, so treat them as the geometric limit rather than a tolerance. No published standard governs media size against part geometry; the ratio rules shown on the tool are trade rules of thumb and they disagree with each other in the margins.
Common questions
Because a part passes through a hole in whichever orientation suits it, not in the orientation that happens to be longest. A rigid convex body passes a circular hole if any one of its projections fits inside that circle. So the governing quantity is the minimum silhouette across all orientations, not the maximum dimension. A 1/4 inch diameter by 1 inch long cylinder has a largest dimension of 1 inch, but end-on it presents a 1/4 inch circle and falls through a 5/16 inch hole without touching the sides.
No. For a right cylinder the minimum silhouette is the circular end face, so the pass-through diameter equals the media diameter regardless of length. A long cylinder and a short one of the same diameter pass exactly the same holes. Length affects how the media behaves in the bowl and how it reaches into recesses, but not whether it fits a hole.
A blind hole has no exit, so passing through is not an escape route. Anything small enough to enter has to come back out the way it went in, which is how blind features pack with media and compound. For blind holes the only safe strategy is media sized above the feature so it cannot enter at all. The calculator never returns a pass-through verdict for a blind feature.
Yes, and this is the failure mode most selection guides ignore. Media loses linear dimension over its service life, so its pass-through diameter shrinks with it. A piece chosen safely oversize migrates downward as it wears and on the way to falling through it passes through the size range where it wedges. The calculator reports the wear fraction at which a currently safe selection first reaches your hole size.
No. Nothing published governs this. What circulates are vendor rules of thumb, commonly at least 1.5 times the hole to resist lodging, twice for margin, or below a third of the hole for free pass-through. Those rules disagree with each other in the margins and all of them compare a single dimension without accounting for orientation. They are shown on the tool for comparison and labelled as rules of thumb, not as standards.
Send us the part
If the calculator says it does not fit, MFI can tell you what will. Send the drawing, the material and the volume.