Abstract: A clamp for fastening a trackball-containing shell to laptop computer keyboards. The clamp has (a) a tray having a dovetail formed thereon for engaging with a dovetail slot formed in the trackball-containing shell, (b) a replaceable first clamping element having a first jaw being insertable in a clearance between keys and a margin of the keyboard, (c) a spring-biased second clamping element having a second jaw for abutting the margin and (d) a button linked to the spring-biased second clamping element. When the button is pressed, the second jaw of the spring-biased second clamping element is accordingly moved away from the first jaw of the first clamping element so that the margin can be sited therebetween. When the button is released, the first jaw of the first clamping element cooperates with the second jaw of the spring-biased second clamping element so as to clamp the margin, so that the trackball-containing shell is firmly maintained in position relative to the keyboard.