The tremlock
This page will explain the advantage of having a tremlock, how the Fender version works and how it differs on the Ultimate Vibrato.
Why is the tremlock so useful
Some Fender Jaguar and Jazzmaster vibrato units have a tremlock which, when engaged, will prevent the floating tremolo plate from moving upwards whilst keeping it in a mid position of its overall travel. Although it can still be pushed down by the tremolo arm the tension of the spring will prevent it from just dropping down, so effectively stops any movement whilst playing if you do not want to use the vibrato function.
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When the guitar is tuned with the tremlock engaged, and the tension spring is adjusted so that the floating plate will stay in the same position after the lock is released, it means that the floating plate will always be set to an approximate mid position of its travel and the height of the tremolo arm above the scratchplate will always be constant after re stringing and tuning.
Also if a string breaks during a gig the reduced tension will make the floating plate raise slightly causing the remaining strings to go out of tune, by re engaging the tremlock in this situation they can be temporarily returned to the correct pitch.
How the Fender tremlock works
On the underside of the Fender unit there is a brass disc which can be slid under the floating plate when the tremolo arm is depressed, this is done with a button on the upper side.
How the Ultimate Vibrato tremlock works
We have stripped down the underside to show this more clearly
On the underside of the Ultimate Vibrato with the floating plate removed you can see the locking bar in the middle.
With the floating plate laid in its normal position when unlocked it can pass over the locking bar
The locking bar now in the lock position
With the floating plate back in place it now will not pass over the locking bar