Hi all,

I thought that the minimum requirement is precise straight lines to make clear diffraction spikes and that it may be possible easily with fine fishing line.

full size image here:
http://farm4.static.flickr.com/3132/2852140265_0cfd4dd761_o.jpg

You can see two sets of diffraction maker.
The left is for my refractor. This is made of fine fishing line and a round toy badminton racket for kids.
You see a sample here:
http://www.johnlewis.com/230417814/Product.aspx

The right is for camera lenses. This is made of the same fishing line, alpha-cyanoacrylate adhesives, and a cheap round towel ring.

Setting was easy and cheap with Scotch tape.

This is a 100% crop showing the spike with the racket and my refractor at F3.6.
The lines are a little bold. I suspect it due to the fact that the racket is not exactly round.

original full size image here:
http://farm4.static.flickr.com/3123/2852974740_be6c930574_o.jpg

This is a 100% crop showing the spike with the towel ring and camera lens at F2.8.

original full size image here:
http://farm4.static.flickr.com/3238/2852141549_9e03c469ac_o.jpg

Thanks Dennis Sakve,
I could be confident about focussing for the first time.