This question of mine, about a cheap replacement for a fascia roll, was closed, apparantly "because it is about how to build your own equipment." I'm sure the closer will eloborate.
I'd argue that questions of the type "what can I use for " or "what properties does a proper have" are on topic. We don't always have a specialist on hand to ask wether the knee brace we bought is good or not, or what to look out for when buying a flexibar or whatever.
To be clear, questions about actually building stuff I don't see on-topic here. But the properties or specs to which one builds yes. So if we were talking about surgical equipment, the question "what maximum surface roughness is tolerable in surgical steel" would bo on topic, then the poster would have to ask a machinist on how to achieve this roughness.