Vacuum Hoses

I was recently looking at my vacuum hoses while I was changing plugs and wire and I noticed that they were quite old. I am wanting to replace them but in my repair manual it states they are all different sizes. I figured they were a universal size with different lengths. Could anyone say for sure?

they are probably 2 or 3 different sizes. but a parts store should have every size in bulk lengths. its a good idea to keep vacuum hoses in good shape, as vacuum leaks can cause bad driveability problems and bad gas mileage.

how often should you replace them?

theres no set time, just look and make sure none are cracked or cracking at all. bend each one some to make sure that they arent hardened. if you crack one by bending it, thats good thats what your looking for. time to replace.