How can I stick a part to a bone?

I have made an Arms Rig in Blender and imported it into Roblox Studio. Here is an Image. I animated the rig in roblox studio. Now, I just have to stick the tool (Gun) to my Arm rig's Palm.

But the problem is, the palm of it is actually a bone. This is an Image of it in explorer. The RightHand in image is the Palm that should stick to. I tried using a WeldConstraint but it says that bones are not compatible.

Any help/opinion would be highly appreciated. Thanks in advance!