Strings made with wrap wire wound upon round core wire need an edge to grip the core wire to prevent the string from going dead and losing intonation.
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Round core wire, by definition, has no edges.  Hexagonal core has 6.  So, at DR Strings we flatten the round core wire to create an anchor for the wrap wire to grip the core wire.
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We flatten a small section of the core wire at a spot that should lie past the nut at the top of the fingerboard and between the tuning machines of your instrument.  This flat section provides and anchor for the wrap wire to grip the core wire.  You should be able to feel this flattened area between your fingers as you touch the end of the string opposite the ball end.
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Without the anchor the string is likely to unwind, go "dead", and fail to intonate properly.
If you need to cut or trim your strings between the anchor (the flattened section) and the ball end, carefully and severely bend or crimp your string as illustrated.  The severe bend (crimp) will provide an anchor for the round core.
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In some instances, properly installing the strings and then cutting/trimming the excess wire will suffice to avoid wrap wire coming loose from round core wire.
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*Applicable to all round core strings.