The mount you probably have seen already, but now the cheapest on the market! Yes sir you heard it right, you can get these puppies for $15/20 a piece! Okay I lied the shipping is $3 USA $13 International.
Copy paste of everything I have written:
Introducing the Boardnamics Caliber II Motor Mount, an essential piece to your DIY electric skateboard build. This is the foundation of the entire drive train, responsible for mounting your brushless motor and aligning the timing belt to the wheel. Built and designed from the ground up to be reliable in rough conditions, this mount features CNC machined aluminum pieces. Made of 6061 T6511 aluminum which helps cool the motor and provide strength all while being lightweight. Nylon lock nuts prevents loosening from vibration during riding.
The slotted design allows this mount to be rotated and flipped in any direction you want. It IS reverse mountable.
The non idler lets you choose between 2 different arm pieces, 50mm or 63mm depending on what size your motor is. 63mm bolt holes are 44mm diagonally, 50mm are 30mm diagonally.
Idler Version: The idler version of the mount features an adjustable idler tensioner that was once a first of its kind back in 2017. An idler pulley changes the path taken by the timing belt in order to engage more teeth on the motor pulley. This results in increased torque transfer without the skipping often seen with high power/fast acceleration setups. For setups that want the very best power transfer possible, this is the better choice.
Arm Thickness: 6.35mm (1/4")
Clamp Thickness: 9.6mm
Weight: 63mm Edition (177g) 50mm Edition (159g)
Center Distance: 70mm ±8mm
Recommended Belt Length: 255mm-275mm
Aluminum Pieces: x1 Arm (50mm or 63mm) x2 Clamp Bracket
Hardware: x4 M4 x 20mm 12.9 SHCS x4 M4 A2 SS Nylon Locknut x2 M6 x 40mm 12.9 SHCS x2 M6 A2 SS Nylon Locknut x4 M4 x 8mm A2 SS Torx
Idler(Idler version only): x1 M8 x 40mm 12.9 SHCS x1 M8 a2 SS Nylon Locknut x2 608-RS Bearing x1 HTD5M-12mm wide 320mm Belt x1 HTD5M-12mm wide 325mm Belt
Lowest price offered here: www.boardnamics.com I know my website is super unfinished but hey, it works!
You can also buy on ebay/amazon for an added $2 due to the fee they set in place.