This post is a small masterclass in fastener design constraints. The poster has a deceptively specific need: they want to limit travel inside a threaded blind hole without a visible jam nut spoiling the aesthetic. Their ideal part is essentially an "anti-nut" — a tube with internal hex drive running all the way through, external threads on the outside, and a length shorter than any commodity set screw. With 32 comments, the thread becomes a tour of why such a simple-sounding part is surprisingly hard to source.

Several useful concepts come out in the discussion:

• Why set screws have a minimum length. Standard set screws (ANSI/ISO) need enough body to fit a hex socket of sufficient depth to transmit torque without rounding out. Once you go shorter than roughly the diameter, the hex socket either bottoms out or becomes too shallow to drive reliably.
• The "threaded insert" alternative. Commenters point out that threaded inserts (helicoils, Keenserts, brass press-ins) are effectively hollow externally-threaded tubes — but their threads are designed to grip a tapped host, not act as a positionable stop.
• Standoffs and threaded couplers. Hex standoffs come close to the "anti-nut" concept but are usually too long and have external flats rather than smooth cylindrical threads.
• Custom machining is often the real answer. Several commenters note that below a certain size, McMaster and Misumi stop carrying parts and you're looking at a screw-machine shop or making them on a lathe by parting off threaded rod and broaching a hex.
• Drive alternatives for short fasteners. When a hex socket won't fit, options include slotted drive, spanner holes, or pin-spanner faces — each with tradeoffs in torque capacity and tool availability.

What makes this post quietly educational is that it forces you to think about why the standard catalog looks the way it does. Fastener dimensions aren't arbitrary — they're the outcome of drive geometry, thread engagement minimums, and manufacturing economics. When your application falls outside those constraints, you usually need either a creative substitution (insert, standoff, custom-cut threaded rod) or a custom part.

It's also a nice example of the value of niche subreddits: a question this specific would drown on r/DIY, but r/Fasteners delivers thoughtful, experienced answers.