Why can't i Autostrut?

[quasarrgames]

There is no Autostrut function on any parts in my vessels. If i right click on a fuel tank, it only shows the sliders for the fuel it contains. If i right click on an engine, it only shows the sliders for thrust and gimbal, and the button to toggle gimbal. There is no button to toggle autostrut, as i've seen in the devnotes. I am using prerelease version 1500, which i know is not the latest version, but i know autostrut was implemented in versions before this one. 

Is there a setting i didn't see initially that i need to turn on? Do i need to install a different version of ksp? does it happen automatically? (i wouldn't think so, given that my crafts don't seem any stronger)

Also, does using autostrut cause the same amount of lag as strutting a ship automatically, or does it cause less lag? 

Thank you in advance

[FullMetalMachinist]

1 hour ago, quasarrgames said:

Is there a setting i didn't see initially that i need to turn on?

Yep, it's one of the new Advanced Tweakables. Turn them on by going to Main Menu -> Settings -> General -> Advanced Tweakables. It's right above the new slider for Default Pre-launch Throttle.