Unlike the X axis, the Y axis idler is supported on one end to the acrylic middle plate. This arrangement places a pretty good load on the acrylic and I noticed some flex as the Y axis would change direction. I designed the bracket to fit over the head of the Y axis idler bolt and attach to the two top screws of the rod cover.
Please note, this part is dimensioned for a stock ToM. My ToM Y axis rods a slightly longer than the body and make the body bow out. I've seen others comment on this so I know I'm not alone.
Also, I'm not implying that this is a defect in MBIs design, the acrylic may be happy with this for years without problems.
Print the part and drill out the holes. The hole for the idler bolt is 9/32", work your way up to this so you don't change the location of the hole. The two rod cover bolt holes are 1/8"
To install just remove the two top rod cover screws, slide the part over the idler bolt head, run the screws back into the part. The screws are just long enough to work.