about basic drawings 2D and 3D: measuring and scaling

Hello again,

I have some questions about basic drawing:

1) how to find parallel or perpendicular points along a curve at a determinate distance and place a mark there. Or in general how to mark points at a distance from a known object?

2) I noticed that sometimes blocks are much smaller or not with the wanted proportions, is just a matter of scaling or is that possible to modify for example the length of a bolt.

3) from the Helix command how to properly draw a Bolt or screws, can you suggest something to read on it?

Thank you very much,

Re: #3. Try this for starters.

http://www.cadtutor.net/forum/showthread.php?51078-Links-to-tutorials-about-3D-bolts-screws-and-threads.&highlight=threaded+bolt

Re: #2. You might want to check out Dynamic Blocks for that bolt. It offers much more flexibility than a normal block.