im new to archery. so new, that i bought a bow that didnt have a rest. a buddy of mine gave me an older model cobra rest. i cant find any installation instructions on the web. does anyone know of a link to the instructions? or can you give me a quick rundown on what i am supposed to do? i have it installed, but i am unsure of the amount of springiness the prongs should have.

the rest looks like this.

have ya tried it out yet?  had same one on both my bows, liked the way they set up, was acurate rest, only reason switched, see the drop away rest's...  after reading what M4Maddness put in here, think had mine set too heavy...  it did hit accuretly,  but believe what M4Maddness says makes sence, as drawing arrow back, less weight on rest, making it lift,  making it a form of drop away...  so to M4Madness Tip me hat  may do some switching around again....

I just went back to an old school prong rest as a celebration of K.I.S.S. and being tired of fidgeting with drop-aways and their unsightly pull string and bit of added noise.

Some more instructions:

You will only be able to use straight fletched arrows (with maybe just a tiny bit of offset).  I use NAP 2" QuikSpin vanes.  These are fletched straight and produce more spin than helical fletched feathers.

You need to turn the nocks on all of your arrows so that the cock vane points down, so it passes between the two prongs.

You want to adjust the width of the prongs to match the diamter of your arrow (it's easier to do this with the rest off the bow).  You want the tips of the prongs to be touching the arrow shaft exactly between the vanes.  About 2/3 of the arrow should be above the tips of the prongs.  Then you will have no vane contact with the rest.

Set the rest up for center shot, so the arrow is passing across the Berger hole (rest mounting hole) and nock point is even or up to 1/8" high.  Make sure the tiller of the bow even.  Then paper tune.

If you have a persistent right or left horizontal tear that you just cannot tune out regardless of how far you move the rest (and you are sure you don't have vane contact by putting red lipstick on the vanes and looking for red streaks on the bow, cable and rest), then remove a twist to the cable yoke that's on the same side as the tear (you will need to press the bow) and add a twist out of the opposite side of the yoke.   Keep adjusting until it shoots bullet holes with the rest at centershot.