Best way to model symmetry

I am working with an assembly that has symmetry in two of three directions. I am curious about the members' thoughts on the best way to model this.

For example, if I were to need a mounting block on both sides, I would model the one and then use "mirror3d" to get the other one. But if I have a bolt that has no orientation and I need to have an evenly spaced series of six bolts per mounting block, then what is the best approach? And not necessarily for time, but for file size. I might draw one and then do a 2x6 array. I might array 1/2 or 1/4 of the pattern and then do a 3D mirror later when I have all my components ready for symmetry. Or I might array the one side of bolts and later do a copy to the other side. Or if it is just a couple and I am working in the proper view, I might just do a copy with the multiple option.

I'm asking because in my work yesterday, I had to modify one feature of the desing. In an effort to clear the area so I could better visualize what needed to be done, I deleted the six bolts from the one side of my model and the file size dropped from 19 MB to 10 MB. The file size has been jumping all around, and I got to wondering if AutoCAD knows how each object got where it was and the way it got there affects file size, or maybe once an object is somewhere then AutoCAD doesn't care where it came from. I know that XREFs would help with file size and I'm working on learning more about them as well, but even so, knowing the best practice to place symmetrical objects would be helpful. Thanks!

If you're not already doing this, use blocks to your advantage. If you created a bolt, make it a block, and then copy and/or mirror the block. Blocks help to keep file size down. Xrefs will also help, but as I mentioned in one of your other threads, you need to upgrade your RAM. 1GB is not going to get you very far in the world of 3D.