parotts beak budding or grafting knives work quite well for me. Steve in Stevens County

I use the best big sharp chopping knife in my kitchen. Dedicated chefs might cringe, but the sharper the knife the easier it is.

I use a single edged razor blade. They are cheap and easily
handled. You can buy them in a hardware store with small
"HOLDERS" attached. They are very sharp and cut easily. Use
a small tack hammer to get thru the heavier parts. A hobby
blade with hobby handle also works well.

Ignore all previous suggestions and buy the bonsai scissors that are made in Japan. Lobaugh Dahlias and Verrones Dahlias sell them. Specifically they are "Garden man Pruners" made by the Kengyu company in Japan. They are about $14.00 plus shipping. Knives of all kinds will work but you will inevitably cut yourself. The bonsai scissors do all of the work of a knife and do it faster, better. You can divide tubers clumps in much less time with them. By the way if you insist on using a knife, invest in a metal glove used to filet fish to hold the clump as you cut it. Knives are very dangerous.

I like to use x-acto knife. Cindy

I love the Gardenman Scissors too, which I bought form Lobaughs.

The handles are a flexible vinyl that is easier on the hands, and the long pointed blades get into the tight spaces. Also, you can sharpen the blades when they get dull. I use mine for everything and have multiple pairs.