I have a necchi 4595, and well I cannot figure out the straight stitch....the dial doesn't show one?

If you haven't removed the top to clean and oil the cams then likely they are stuck, hence zigzag.

Generally speaking; You should have two setting bars on your machine, one for the stitch size and one for cotton tension (might be close to needle part, above)...you will see it has numbers you can set it to the level you want. I hope you find this useful.

since you bought the machine at a state sale it would probably be a good idea to have the machine serviced.
you should be able to go from straight stitch to zig zag with out any problems.
if you move the dials or knob & the machine will not do a straight stitch then it needs to be checked

try changing the needle, and make sure bobbin is in correctly

Try the Necchi Yahoo Group. There are members who often sell parts and they also are very knowledgeable and helpful.. You should also try eBay. They have parts for lots of vintage machines. You may not find what you are looking for right away but look often as things show up everyday.
https://groups.yahoo.com/neo/groups/Necchi_Pfaff_Sewing_Machine_Collectors/conversations/messages?messageStartId=9&archiveSearch=true

Contact Necchi directly (800-525-9987) and speak with the Service manager who may be able to get the part for you if they are available anywhere.
sewman7

does anyb ody have a manual i can download

Try moving the stitch length dial to 4 or 5 - check the manual. You may have it in the position for very close together sewing. I had to do a lot of trying with my 4795 to get it to work right. I found that very thin thread, polyester kind, broke at the needle after a couple of stitches. I switched to coats & clarks thread and a Singer ball point needle and it works fine. Be sure your needle is inserted with the flat top toward the back of the machine. Good luck!