Choose how STEP surfaces become a mesh
Decide how CAD surfaces become triangles before you export. Set linear and angular deflection, compare the triangle counts they produce, and inspect the preview. These are the real kernel settings, not a slider over a fixed result.
Control how CAD surfaces become a mesh. Your file stays in your browser.
What the two numbers do
Linear deflection is how far a triangle chord is allowed to sit from the true surface, in millimetres. Angular deflection is how much the surface normal may turn across one triangle, in radians. Tighten either and curved faces get more triangles.
The preview shows the mesh you would export and the count it costs, so you can compare two settings on your own part rather than on a rule of thumb. A cylinder is where the difference shows first.
What these numbers are not
They are requested kernel settings. They are not an independently measured error bound for your file. The kernel treats them as targets while meshing, and this site does not then measure the result against the original surface and certify a deviation. Anyone quoting you a guaranteed tolerance from a deflection value is quoting the request, not the outcome.
The conversion is one way
Triangles do not become surfaces again. A hole that was a cylinder with a radius becomes a many-sided prism, and no later step recovers the radius. Keep the STEP or IGES file. If someone downstream needs exact geometry, send them that rather than the mesh, and see STEP to STL for what the conversion carries.