I would first recommend that you go to the top of the page and click on "Accessories"
go down and you will find " tripods and other riggings "
there you will find links where members have reviewed various tripods and other equipment
"acra " probably refers to the acra swiss quick release system
' 1) Arca-Swiss Quick Release
The Arca-Swiss quick release system is based on a two piece mechanism. The first piece, generally referred to as a “plate”, is attached to a camera or a lens (or any other device). It comes in a standard, “arca-style” 35mm wide form with a 45° dovetail and can vary in length (a sample plate is illustrated above to the right of the tripod head). The second piece is the mounting base, generally referred to as a “clamp”, where the plate gets attached and secured. The clamp can be fully opened, allowing the plate to be dropped in and secured, or can be partially opened to allow the plate to be slid into the position. The biggest advantage of the Arca-Swiss quick release system is this ability to slide the plate without having to worry about mounting or dismounting anything. The 45° dovetail on the plate, as pictured below, allows equipment to be moved across the clamp and secured in a specific location using a side knob or a locking release. . . . "
What is Arca-Swiss Quick Release System?