The Peltor Sport Tactical 500 Electronic Hearing Protection Ear Muffs w/Bluetooth will most likely not fit under a helmet.
You disable the Bluetooth by disconnecting on the source device (like your phone) , just like every other Bluetooth headset.
You would need to adjust the volume on the bluetooth connected device. The volume control on these would control the background noise only.
This headset will have one microphone per ear.
They do not have a mount on them. They are intended for wear over the head.
The Peltor Sport Tactical 500 Ergonomic Ear Muffs is foldable and completely adjustable for comfortable fit. There is not a size chart provided.
Yes, you can plug them in as headphones while still leaving on the sound suppression and amplification.
It lowers the volume to a quieter level that is safe for your ears.
These are stereo.
3M/Peltor has not provided that information even on their own site. We recommend contacting them directly, they should be able to provide you with that information. You can reach them here: https://www.3m.com/3M/en_US/company-us/help-center/