This mounts are designed to sit the fans within the chassis, but only at an 8mm depth - this is deliberate to give more space between the motors and the fan to maximize airflow, and also to allow as much clearance as possible for the wiring loom. I have some low profile fans (only 10mm depth on a 60mm fan) on order, and they will sit more or less flush with the bottom of the printer once fitted.The ones shown in the pictures are standard 60mm fans, and have an overall depth of 19.5mm, so protrude under the chassis. If you don't want to find low profile fans, please ensure that you have printed feet for your Simple and installed prior to installing these fan mounts. I use these:http://www.thingiverse.com/thing:506959There are two types of mounts included here - the ones in the pictures - these are plain, and contain two mounting points for 60mm fans (central, and towards one end to focus on the stepper drivers in my case). The second design is identical except it contains vents, which reduced the amount of plastic required, and may give better airflow depending on your fans design. My suggestion would be to go with the vented option (version 1.1) first off.As mentioned above, the mounts are designed to friction fit within the chassis, once the fan has been mounted. A dab of hot glue maybe required at each end if you get any material retraction.Print off two mounts for each fan to be installed, and ensure that you print them on their sides to avoid any support material requirements.