9.5" Height Rigid Steel Edging - Weathering

What is the length of the pre-formed corners?

They are 10 inches each side of the 90 degree bend.

What is the difference between joining plates and spike nails that are included and the joining sleeve/hardware that has to be purchased separately? Are these the same? If I bought 4 sections with two corners to form a three walled box what do I need to purchase on top of that besides anchors?

The spiked nails are long, spiked nails that go into the bottom lip of the edging into the ground to secure the edging.  5 per section are included in the price of the edging.

Each section comes with the connector plates used to connect the edging together.  Also, included in the price of the edging.

Joining Sleeves are used only when you need to cut the edging and then want to reconnect it.  When you cut the end off of the section, you have then cut off the pre-built in connector pieces.  Therefore, you would need a joining sleeve in order to reconnect it.  If you are not making an cuts, then you don't need a joining sleeve.

In your example:  4 panels and 2 corners (with no cuts) the only thing you need to purchase are the sections and anchors posts.  2 per section recommended.
(4) 7'sections
(2) Corners
(8) Anchor Posts

Can you cut Straightcurve’s 9.5” Ridgid weather steel to a desire length?

Yes, an angle grinder is recommended to cut the edging.  If you cut the edging and then need to reconnect it (if you've cut off the built in connectors) then you would need a joining sleeve.  See video demo below.

When to use a joining sleeve

Can I shorten on ridgid steel edging and form a 90 degree corner ?

Hi,
Yes, to make a 90 degre corner, you would need to use an angle grinder to make an intermittent score line and use a mallet to hammer into place.  Please see the below video for reference.  To shorten the edging, an angle grinder is recommended as well.

how to make a corner with the 9.5" edging

Thanks
Erin