My mailbox flag bracket was looking old and worn out so I modeled a replacement. The space between the two holes on the mailbox is about 17mm, not sure this is a standard part. The way the original part is locked into place, with a wedged piece, isn't ideal for a 3d printed part, so this replacement has threads and a nut to hold it in place. I haven't had any issues with it coming loose so far, the grommets help keep it in place, but be careful not to overtighten it.
My mailbox gets a lot of sunlight, so I printed it out of ASA for it's UV resistance. The grommets are printed out of flex material. It's been working well for about a month now, though admittedly the flag doesn't get much use here...
The author marked this model as their own original creation.