SieMatic rail mount part
This is a 2-part plastic subassembly used to connect the rail to the cabinet wall. The butterfly-shaped plug is inserted into a channel in the cabinet wall, at the desired height, and then the part is rotated 90 deg. to lock. The rail is then attached using the metal screw.
Several of these broke due to overload.
Thanks for reaching out to us. I'm afraid we don't have anything like this. Based on your description, this sounds like a somewhat specialized part. You often have to go directly to the manufacturer for this kind of thing.
That said, we have a couple different parts that sort of fill the same niche. These are drawer track spacers that connect the track to the wall of the cabinet. They're just pieces of plastic, though, there's nothing about them that turns to lock or anything. See our 32-334, 32-339, and 32-350 for our three sizes. I can't say for sure, but if all you need is for the track to connect to the wall, then one of these may be worth considering.