This section is for discussion of Flex Plates that will work with the 713Maker custom mag beds for the RailCore II 250 & 300ZL Printers: https://713maker.com/railcore
The build plate size is significantly larger than the printable area. On the 250ZL, for instance, the bed is 275×281, but 250×250 is about the max printable area. You can approach this problem in different fashions.
The most convenient is to get a flex plate that's 5-10mm longer than the width of your build plate and the full width - i.e, on the 250ZL, 280×280 would fill the build plate and provide a 5mm lip to lift it off with.
You can also, less elegantly, purchase a flex plate the size of your printable area (250×250 or 300×300). You can eyeball it, or mark your bed in some fashion with alignment marks. This works, but some may find it inelegant. The magnets in the 713 mag bed are *strong*, so you will want to make a tab (Kapton tape works well) in one corner to allow you to lift the flex plate off the magbed.