For anyone who has not used a Japanese waterstone before then a combination provides a good introduction. Size 200 x 50 x 25mm.
Made to hold waterstones up to 210mm(8.1/4") in length. Rubber holders at either end, one fixed and one sliding, which can be tightened by means of two knurled screws to hold the waterstone firmly but gently. A central rubber block provides extra support. Grips on the underside prevent your waterstone walking away whilst you are trying to sharpen a blade. Also suitable for oil stones and diamond stones.