What on a #6 prop holds the nylon bushing in place to keep from sliding forward into the shaft bearing ?

You need a keeper which is a flat plastic split ring.

http://bblades.com/shop/accessories/...etaining-ring/

That is what I thought ,what can be done if there is no grove for the ring to go into ?

There has to be a groove or you have a very old tapered version propeller.

Brett

Some of the old props didn't use a sleeve, stainless hub ran directly on the propshaft. It was hard on propshafts, the sleeve helps and it allowed for one prop bore to fit #6 and 3,4,5 propshafts with different thickness sleeves.

There is no groove that I can see , If it was an old version what would the inside dimension be ?

Don't remember the propshaft diameter but the prop bore would just slide over the shaft with little clearance. How old is the prop, Merc Racing prop or other?

I have no idea who manufactured them or how old they are , the info stamped on the hub is 174F 35 C5 They are a 4 blade with 1.875 id and no tapered that I can see ,tip to tip they are 16.875 with a 15* rake

1.875 id is the correct id for a direct fit on a Six propshaft, no room for a sleeve. Could be an early Kiekhaefer or other manufacturer on the prop.

What is the od of the nylon bushing ?