A customer sent me this last month:

"I need an SFU1605 for a 100 kg table. Will it work?"

I didn't answer right away. Not because I didn't know, but because the question as written can't be answered honestly. A 100 kg table on a horizontal axis with proper linear guides is a very different problem from a 100 kg table on a vertical Z-axis. Same screw. Same weight. Completely different result.

And that's the thing about SFU1605. It's one of the most common ball screws in small CNC and automation, and it's also one of the most misunderstood. People see the model number, look up a load rating, and assume that number is the answer. It isn't.

So let me explain how I actually think about it—not from a catalog, but from machines I've built, fixed, and in a couple of cases, watched fail.