What is this piece / cover delivered with the STECS Space Throttle Standard?

[Sebastian]

I just received my STECS Space Throttle Standard, and I am very happy so far.

Among the accessories I found this little cover (?) that I can't figured what it is.

Is it a "leftover" from the STECS base or STEM module, or what is its purpose?

[Ron61]

Watch this video at 1:30.

[Sebastian]

Alright, I see - so mine has the adapter plate for the MFH pre-installed already. I thought it had to fit somewhere around there, but couldn't quite place it.

Thanks!