Picture Hanger Wall Hook Mount Holder

I bought a great picture but got no free space for it at any wall.. But free space on a sloped wall... So i needed a solution to attach the picture to a sloping wall. Here's what came to mind. A pin and a mounted gap where the pin can slide in and hold. Keep it simple and stupid. Well.. The only stupid thing is that it's not that easy to attach.
That's the way i managed it:
Mount all screws with the pins to one side (i used the frameside, wall side sould worked also) and one slider to the oth