I have a back up prop the numbers on it match on the front is 48 and on the end 19p its on both props but numbers inbetween dont match do you think this is the same prop.

I've never seen a number like 48 on a prop.
Usually its the dia X Pitch. Like 15X19......

The 19p is your pitch. Compare the diameters, put it on the lower unit and turn it by hand, and make a measurement.

48X19...sounds like my pants size:laughs:

It sounds like you have a Mercury. The 48 would be the first two digits for the part number and the 19p is a 19pitch.
These two links should help.
mercury parts (http://www.mercurypartsexpress.com/PartsExpress/ProductSelection/ServiceParts/sphome.asp?CID=)

mercury prop selector (http://www.mercurymarine.com/prop_selector)