PRO LT Handlebar Stem asks to tighten top handlebar screws first before bottom screws? Conflicting manual instructions?
Here are a few diagrams I drew in Autodesk Fusion 360 to explain how these zero-gap stems work.
According to the instructions provided with the few zero-gap stems I've encountered, you should tighten the &quot;no gap&quot; bolts to full torque first, then alternate between the lower bolts to fasten the handlebar. That makes sense according to the diagrams because that ensures the upper tabs are solidly clamped together to form the C-shaped clamp. If you're confused by my weird terminology, take a look at the diagrams (especially #3 and #4). You'll see what I'm talking about.

This is a normal stem. The left piece (the stem's faceplate) evenly tightens in a straight line towards the right piece. Assuming it gets properly torqued, the faceplate will travel in a straight line to the right as the bolts are tightened.


Next, this is what would happen if you tried to use a normal stem in a no-gap fashion. As you can see, the two pieces are no longer parallel, and the bolt holes are no longer aligned properly. That's not good. If you were to tighten the bolts while the stem was arranged like this, you run the risk of damaging your stem and handlebars because the faceplate will be forcibly bent into an oval shape so that the tabs (and thus bolts) are parallel once again. Obviously, you cannot properly clamp a round bar with an oval-shaped clamp.


The next picture represents a zero-gap stem installed correctly. Note how the upper tabs are flush with each other and are lined up parallel; you're effectively turning the two separate pieces into one solid C-shaped clamp. When you tighten the lower bolt, the top joint will stay still. Instead of the faceplate moving in a straight line towards the right like how it would with a normal stem, it is now deflecting in a circular manner.


And finally, this is what it would look like if you tried to use a no-gap stem like a normal stem. You can see how the tabs are completely out of alignment. Like before, the faceplate might get deformed into an oval shape if you try to tighten it down.


My guess is that with a zero-gap stem, you're basically trying to replicate a classic quill stem's one-piece clamp without the hassle of also having to remove the brakes and shifters when removing the bars. The entire clamp should function as a rigid unit after you tighten the &quot;no gap&quot; bolts.