When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
5 on 5 1/2 is meaning 5 holes for 5 lugs (5 lugs ='s 1/2 ton ='s F150) and 5 1/2" is the measurement from the far outer edge of one bolt hole and across to another far edge bolt hole.
5 on 4 1/2 is the small Ranger and Bronco II rim size.
The difference in wheel bolt patterns arises due to the cost/strength each truck series was designed for.
Light duty trucks (newer rangers, Bronco 2, 87-06 Jeep Wranglers, etc) got the 5 x 4.5". This is shared with many passenger cars (Mustang) and is the "light" pattern. On 4x4 applications, this "light" size restricts what axles the OE could run (For example, a Wrangler Dana 44 front is really a Dana 44 center section with Dana 30 components from the knuckle out!)
1/2 ton trucks got the 5 x 5.5" bolt pattern. The same number of lugs, but a bigger circle - this is to accommodate the possibility of a 4x4 front axle like a true Dana 44.
Heavier vehicles sometimes see 6 x 5.5 - the extra lug for security when a heavy SOB goes around a corner, or has to stop suddenly
3/4 or 1-ton trucks usually get the 8 x 6.5 - enough bolt spacing to clear a Dana 60 front hub, and the extra lugs for the heavy loads.
Was this strictly necessary for the OP's question? Not really, but kind of good to keep in mind if you're buying a newer Truck/SUV.