This kit is designed for a 3" toothpick style X8 octocopter. 

TuneRC Poly F405 2S-4S AIO FC has soldering pads dedicated for M5-M8. Now, anyone can build a toothpick style 3" X8 by adding a 4-in-1 ESC and four motors with this kit.  Even if your AIO FC (F405 or above) does not have soldering pads dedicated for M5-M8, you  can still make an X8 by making resourse remapping LED_STRIP, unused UARTS, or unused SCL (I2C) to M5-M8, and making those pins enable timer and DMA (for DSHOT).

If you want to mount an additional 4-in-1 ESC under the main plate, the Minimal Bottom Plate 1.5mm is reccomended for protecting it.

• FC and ESC Mount : 16x16mm, 20x20mm, 25.5x25.5mm, M2
• Wheel Base : 140mm
• Thickness : Main Plate 3mm, Motor Mount 2.5mm
• Weight : About 16g

As for compatibility with the FPV Cage series, this frame kit with 3" props is compatible only with the FPV Cage for 14mm Cam.