Slow feeder inserts for Great Danes?

Hi, my boyfriend has a lovely Great Dane who eats out of a raised feeder. I found him a slow feed insert, and he laughs at it. It is perfect for my own dog, whose mouth is a normal size.

So I am curious as to if any of you Dane owners have a favorite slow feed insert OR even a slow feed bowl that will fit in the big raised feeder slots.

:woman_shrugging:t3:

Can you post the diameter of the holes for the food bowls?