The "boycott Israel" movement likes to target Caterpillar because Israel has used their equipment to destroy terror infrastructure.
Hamas hasn't gotten the message.
In a new video released by Hamas, they show Caterpillar equipment (0:35) being used to dig in Gaza. The first scene is apparently of them using this equipment to reach terrorists who are caught in a tunnel explosion, and people with Red Crescent logos go into the tunnel to evacuate the terrorists. It is not showing live events, of course, meaning that Hamas commissions Cat equipment for use in propaganda videos, and Gaza paramedics are apparently complicit as well - the ambulance is clearly seen as a prop.
Obviously some construction equipment and materials make it through the "siege" of Gaza.