All steel - unlike the parallel clamps,there are no plastic parts to break (I spun the plastic handle off a Jet clamp and have busted parts on my Bessy's) - the Jorgensen I-Beams may cost more, but in the long run they are a bargain as I'll never need to replace or repair them.  Clamping pressure far exceeds parallel clamps (can close joints the other clamps can not).  I-Beams barely flex.  They will last and work until someone lets them turn to rust, which is not likely to happen.  Made in USA by my fellow countrymen who have a job and support our Nation - Buy American!!!!