Join Date: May 2004
Location: Wilmington, DE
Bikes: 2016 Hong Fu FM-079-F, 1984 Trek 660, 2003 Specialized Hardrock, 2004 LOOK KG386i (RIP), 2005 Iron Horse Warrior Expert, 2009 Pedal Force CX1, 2016 Islabikes Beinn 20 (son's)
Mentioned: 6 Post(s)
Tagged: 0 Thread(s)
Quoted: 432 Post(s)
Whatever you are threading those bolts into has damaged threads. It's possible that the tapped (threaded) piece can be cleaned up using the appropriate tap and still have good enough threads to be serviceable, but it's also possible that the piece has been ruined. The damaged threads were likely caused by the bolts being crossthreaded (installed at an angle which caused the threads in both parts to not mesh properly) by the previous owner.
My suggestion would be to take the threaded part to a bike shop (or machine shop if one is available) and have them clean up the threads with a tap. Throw those olds bolts out as they are worthless now and get some new ones. With the threads cleaned up, attempt to install the parts and torque to spec. If everything goes ok, you're good to go. If you it turns out the bolt keeps spinning and won't torque to spec, then you'll need to look into some options for repairing that component.
As a general note, if a fastener won't thread on easily by hand something is wrong. Do NOT attempt to forcefully thread something together using tools as you'll likely damage something. It's a lesson that just about everyone who spends enough time working on mechanical things learns the hard way.