3/4" heater hose is readily available at any auto parts store and slips over the 2 larger nipples much easier with less chance of hose splitting. The 2 nipples on the heater core r different sizes as the heater hose nipple on the water pump and the heater hose nipple on the stat cover r different sizes.

 

The two larger nipples are 11/16", the two smaller are actually 5/8" ... Worked for me on two vehicles without any hassles so just passing it along.

 

......and several of us were just passing along to the newbie OP that upon close inspection there r 2 different nipple sizes, 2 different size hoses, from the factory and that the smaller diameter hose attaches to the smaller diameter nipples and the larger diameter hose attaches to the larger diameter nipples.

I have yet to find a auto parts store that carries bulk 11/16" heater hose (see post #8) but they all carry 3/4" (12/16") along with 5/8" heater hose. For a newbie stretching the smaller heater hose over the larger nipple may be difficult and frustrating (but it can be done)....and there is an easier way (with less chance of hose splitting)....buy 2 different sizes of heater hose (5/8" and 3/4").

 

Just did the heater valve bypass on my girlfriends Xj. Her heat would get like warm at best. So I flushed the core with a garden hose, removed the heater valve and ran a 3/4" hose and a 5/8" hose to the corresponding spots. It was very easy to fit the hoses over the nipples. After all this the heat blows so damn hot! Burns your fingers if you hold them at the vents for to long.

All in all its a very easy job to do yourself. Took about 45mins with flushing/removing/installing new hoses.