These two numbers show up on almost every molded part, and both are cheap to fix in CAD and annoying to fix once a mold already exists, which is exactly why they are worth learning early instead of after a tooling invoice.
Draft angle: how much taper a wall needs to release
Draft angle is the small taper on a wall that lets a part pull free from the mold without dragging or scuffing on the way out. A flat, zero-draft wall can look fine in CAD and still fail to eject cleanly in steel. Plastic walls generally need 1 to 2 degrees of draft as a minimum. Surface texture raises that number fast: add roughly 1.5 degrees of draft for every 0.025mm of texture depth, so a heavily textured surface, the kind used for a soft-touch or grained finish, can need 5 degrees or more before it ejects without dragging.
Rib-to-wall ratio: why a thick rib shows up as a sink mark
A rib is a thin wall added for stiffness, and if it is thicker than the wall it attaches to, it cools slower than the surrounding material. That slower-cooling spot pulls the surface in slightly as it shrinks, which shows up as a visible dent, a sink mark, on the opposite, cosmetic face of the part. Keeping ribs at 40 to 60 percent of the adjacent wall thickness is the standard way to avoid it, since a thinner rib cools at close to the same rate as the wall around it.
Checking this on an object already in your hand
Pick something molded near you right now, a phone case, a bracket, a keyboard key, and look at it under a raking light along one wall. A wall with almost no visible taper is running close to zero draft. A wall that clearly narrows toward the base is somewhere in the 3 to 5 degree range typical of textured parts. Doing that with a handful of objects makes the numbers above stop feeling abstract fairly quickly, and it is a faster way to build intuition than reading a spec sheet.
Before a design goes out to a mold shop
A molder can flag a draft or rib problem by eye faster than almost anything else on a part, since they see it daily. fabdose checks draft angle per face on an uploaded CAD file, worth running as an early pass alongside that kind of review. Rib-to-wall ratio is still something to check by hand against the 40 to 60 percent guideline above, not something fabdose analyzes today.