For a while now I have been looking for something to use to hold parts in place during a build.
I have used old batteries, baked bean tins etc in the past, but now I have found these.
They are cast iron each 1lb in weight, they can be stacked if more pressure is needed to hold something.
The cost was £0.30 each, but delivery was over £5.00, so I would suggest that if you want to buy some of these then try and find someone to share the delivery cost, I think you can buy quite a few of them before this cost goes up.
The link above is where to find them, you will need to copy and paste it, I haven`t found how to post a live link.