Last updated: 18 September 2026
Some glass shower doors look slightly out of line even though the door itself still works perfectly well.
It may open and close smoothly, the glass may feel secure, and nothing seems obviously broken. The problem only shows up when the door is shut. The gap between the two glass edges may be narrower at the top and wider further down, or the magnetic seals may meet in one area but leave a gap somewhere else.
Before assuming the whole door needs attention, take a closer look at that vertical gap between the two pieces of glass.
If the uneven gap is underneath the glass, between the door and the shower tray, that is a different issue. We cover that separately in our guide to dealing with an uneven gap under a shower door. Here, we're looking at doors where the two vertical glass edges do not quite line up when closed.
First, check whether a seal can actually help
Open and close the door a few times and watch what it does.
If it moves freely, does not scrape against the tray and the glass feels secure, a small difference between the two closing edges may be something a suitable seal can cope with.
You might notice that the glass sits fairly close together at the top, then gradually moves further apart towards the bottom. On some doors, the existing magnetic seals will catch at the top but never quite meet lower down.
That is a different situation from a door that has clearly dropped, catches as it moves or has to be pushed into place before it will close. In those cases, changing the seal alone is unlikely to sort the problem.
Why does a standard magnetic seal only meet in places?
Most standard magnetic shower door seals work best when the distance between the two glass edges stays fairly consistent.
Imagine measuring a closed door and getting 19mm at the top, 22mm halfway down and 27mm at the bottom.
If you only measure in the middle, it is easy to think of that as a 22mm gap. In reality, the seal has to deal with a gap that changes all the way down the door.
That is why you can end up with the magnets meeting nicely near the top while the bottom still sits apart. On another door, the middle may close properly but the contact becomes weaker towards either end.
Simply choosing a wider standard magnetic seal may still leave you with the same problem.
When is M410AC worth considering?
M410AC has a wider flexible section between the part that grips the glass and the magnetic closing edge. That gives the magnetic strip a little movement instead of keeping it in exactly the same position from top to bottom.
When the gap is slightly narrower at the top and wider lower down, that extra movement can help the magnetic edges continue meeting across more of the door height.
The idea came from a problem that kept appearing in real customer enquiries. The shower door itself was often still perfectly usable, but a standard magnetic seal would meet in one area and miss in another. SIMBA founder and engineer James Liu developed M410AC around that problem.
It is mainly suited to doors that still open and close normally, with secure glass, but where the two closing edges sit slightly out of line. A common sign is an existing magnetic seal that catches properly in one part of the door and leaves a gap elsewhere.
If your gap is roughly 18–30mm, the next things to check are the glass thickness and the way the two panels meet. M410AC is available for 4–6mm and 8–10mm glass and can be used where the glass closes at roughly 90° or 180°.
If the gap is already fairly even from top to bottom, a standard magnetic shower door seal will often make more sense.
M410AC is not meant to pull a badly dropped door back into line. It is there for doors that still work normally but have a varying gap that a fixed magnetic seal struggles to follow.
Measure the top, middle and bottom before choosing a seal
This is one of those jobs where a single measurement can be surprisingly misleading.
Close the door fully and measure the gap at the top, halfway down and near the bottom. Keep all three measurements rather than averaging them.
Example: 19mm at the top, 22mm in the middle and 27mm at the bottom.
Keep all three figures. Writing the gap down as simply “about 22mm” hides the part that matters most: the distance changes down the height of the door.
With M410AC, start by checking whether all three measurements sit roughly within its 18–30mm range. Then look at the glass thickness and the angle at which the two panels meet.
A door measuring 10mm at the top and 32mm at the bottom is a different proposition, even if the average happens to fall somewhere in between.
Measure the glass on both sides, too. It is easy to check one panel and assume the other is the same thickness, but that is not always the case.
You will also need to know whether the two pieces of glass meet at roughly 90° or 180°. Gap, glass thickness and closing angle are all useful when working out which magnetic shower door seal you need.
Still unsure? A photo is often more useful than trying to describe the door as “a bit wonky”. Take one with the door fully closed, then a closer photo of the gap near the top and bottom.
If the door still works properly but the magnetic seal stubbornly refuses to meet all the way down, do not write off the whole shower door just yet. A few careful measurements will usually tell you whether the mismatch is something a more suitable seal may be able to handle.