Most scissor jacks don't always stay tight after they are first set.  They can loosen up and may need to be re-tightened. 

Here’s Why…

    1.  Older Jacks that have been cranked with road grime and dirt on the jack screw wears the nut threads down.

2.  New Jacks may be lubricated to turn smoothly - that can also cause the threads to slip and also collect dirt and grime.
 
3.  Normal moving around inside the trailer, especially towards the rear, will transmit pulses onto the jacks and provoke loosening.

4.  Wind can loosen the jacks by trying to rock the trailer.

5.  Blocks under the Jack to reduce sideways wobble, puts a higher strain on the screw, which can induce loosening. The harder it's cranked, the more strain on the screw; the easier it can slip.

   SOLUTION:  The "Nut Lock" will prevent these problems.

And one more problem ... Sometimes the Jack screw can begin to unwind as soon as you pull the crank off.  This is when the
Sizzer Jack Nut Lock "Key" can help.  Here's how...

 The Sizzer Jack Nut Lock is designed for use with typical jacks that have a 3/4" (19 mm) hex crank nut.