The easiest way to get an accurate template made is to cut some threaded rod (or cut the heads of some bolts) and insert them part way into the four holes in the top of the subframe where the rack will mount. Take a sheet of plywood, MDF (or even card, but make sure it's stiff) and tap it gently with a mallet onto the exposed ends of the threaded rod taking care not to move it.

This will leave indents on the sheet which can then be drilled at those points and hey presto, you have a perfect template!

You can also put a dab of paint on the end of each exposed stud to leave a mark if you don't fancy the mallet method.

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