Replace and Fill command with types of planks

i understand planks (that dont have an item title like crimson_planks) are specified by a number in a command line, such as planks 2 and planks 3 etc, but when using any command other than fill, or specifically when i need to replace blocks, i think the space breaks my command; or am i doing something wrong?
for example, i'm trying to fill with this command:
/fill 0 10 20 ~~~ stone replace planks 4

but i always get a syntax error at "ce planks 4". is there a way to bracket the commands? i've tried [planks 4] and <planks 4> as well but nothing has changed. it would be great if planks could get their own item names like crimson_planks and other woods have...is it that difficult to change? that or somehow make the item data number connected so it can't interfere with more complex commands.