What type of weed trimmer? name and model. I haven't seen one like that yet. But, I would think it is spring loaded when you press or bump it it unlocked when the spring is compressed releasing the inter spool and centrifical forces the sting to advance. My second question is did it have string in it? if so, there should be an arrow pointing the direction to wind the string. There should be some hole at the bottom of the string groove to poke the string in to hold it while you are winding it. Hole 3a IMO would be to hold the string while you wind the second spool.

So you would wind the top spool first and lock the string in the hole provided. then you would wind the second or lower spool and lock the string in the 3a hole. Now you would assemble the black outer housing over the yellow spool housing threading the string through the holes in the black housing making sure the spring is at the top. Looks like this model snaps in due to the slots in the side of the black outer housing.

Maybe someone will respond that actually has that type of Trimmer with better instruction than mine cause I just guess based on the two parts you are showing... Rc

The model is a Craftsman Weedwacker 358.791520. I downloaded the manual but the thing in the manual is different from the one I have. So I don't know how much help that would be. Yes there was string in it, and it does have a couple of arrows on the bottow, one pointing at about 9 o clock and the other point at 6 o clock, so I guess I wind it counter-clockwise, right?

What is "the bottome of the string groove"? And yes the model does snap in and is spring loaded. Thanks for trying to help.

Go to www.poulan.com and type MX557 in the box at the top right corner. This will give you a manual that uses the same cutting head.

Typically you would line up the arrows on the assembled unit (without the bump cap) and have two 10' lengths of the appropriate line ready. Push a line into the unit from one side (through the line hole) until it appears from a small hole in the yellow spool. Then the end of the line is bent down into an adjacent hole to lock that line in. Repeat on the other side, replace the bump cap then start winding the spool. Wind up all you can without using force, and cut off the excess. You should be ready to start trimming. Caveat: may not work with all bump-feed trimmers.

Thanks, Sawman! Thats just what I needed. Thanks to everyone else too for trying to help me. Thanks.