Perhaps it means "despacho". Just a possibility.

It's a possibility.

Could it be 'despacho' or 'despachado' meaning when the part was sent?

As it's I'd say it's a noun, and could be a verb if it came under the heading, which it doesn't

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Note added at 6 hrs (2012-02-10 21:34:48 GMT)
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I meant to say As it's A HEADING I'd say it's a noun, and could be a verb if it came under the heading, which it doesn't

"Desp." stands for "desperdicio", I believe.

Many similar invoices/costings with a column for "Desp." can be found on the Internet. A number of them indicate that the figures in this column are percentages, with the column headad "Desp. %". For example:

"UND - CANT. - DESP.% - PRECIO UNIT - VALOR TOTAL"
http://www.contratos.gov.co/archivospuc1/2011/DA/276834011/1...

Here's another example, where the figures are eg. 5.00%, 3.00% 2.00%:
http://www.contratos.gov.co/archivospuc1/2011/DA/217001022/1...

This column is often blank, anyway (as in your document); figures appear there only for certain items. Only certain items involve wastage.

Here is a list laid out differently, which identifies "desp." as "desperdicio". The columns are "Concepto, Cálculo, U.M, Cant. Muestra, Cant. + desp.M2":
"Lamina USG Sheetrock de 1/2" - Área pared x 2 + 5% desperdicio - m2 - 26.57 - 2.10"
Postes metálicos Panelrock - (11x2.44)+(2x0.44) + 5% desp. - ml - 27.72 - 2.19"

So the desperdicio is expressed as a percentage and this is added onto the basic quantity to give a gross requirement, allowing for wastage.

Here's another example which similarly uses both "+ 3% desp." and "+ 3% desperdicio":
http://books.google.es/books?id=f8G8UFFjd9sC&pg=PA129&lpg=PA...

Here's a similar document in English, which refers to "% wastage":

"1. Bricks Traditional Bricks(9"x4.5"x3") Nominal size i/c 5% wastage nos. 1.40"
http://www.ensoftsystems.com/slideshow/RateAnly-SalientFeatu...

(It's impossible to set out these tabular examples clearly here, so it's best to look at the original documents to get an idea.)

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Note added at 2 hrs (2012-02-10 18:26:12 GMT)
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Here's a good example to illustrate how it works. Item 1 here is "PINTURA DE ESMALTE TIPO A". Und. (unidad) is "gln", Cant. is 0.25000, Desp. is 5.00, Precio is 170.00 and Total is 44.63. So this is one quarter gallon of paint at 170 per gallon, which comes to 42.50, plus 5% for wastage, which brings it up to a total of 44.63.
http://www.scribd.com/doc/59647747/Analisis-Cloacas

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Note added at 7 hrs (2012-02-10 23:11:21 GMT)
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I have just realised one of my references is missing its URL. The third document quoted, which identifies "+ 5% desp." as "+ 5% desperdicio", comes from:
http://www.construdata.com/BancoConocimiento/A/analisis_livi...