This is a type of "tack" and, going from the context ("cadenas", especially"), I'd say their talking about the typical "studs" that decorate (leather) jackets, etc.

Pls see:

tacha | English | Dictionary & Translation by Babylon - 4:40am
tacha. Dictionary terms for tacha in English, English definition for tacha, Thesaurus and Translations of tacha to English, French, Italian, Spanish, ...
www.babylon.com/definition/tacha/English


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Note added at 9 mins (2010-06-05 12:46:18 GMT)
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Tacha English Spanish Translation | Traductor ingles español
A sort of small nails, somewhat larger than tasks. (f). Sano y sin tacha -> sound and without blemish. verb. 4. TACHO. Poner tacha -> to make objections ...
www.spanishdict.com/translate/tacha

tacha - Spanish translation - bab.la English-Spanish dictionary
Translation for 'tacha' in the free English-Spanish dictionary and many other Spanish translations.
en.bab.la/dictionary/english-spanish/tacha

tacha - Diccionario Ingles-Español WordReference.com - [ Translate this page ]
tacha - Traduccion ingles de diccionario ingles. ... Visit the Spanish-English Forum. 'tacha' also found in these entries: English: ...
www.wordreference.com/es/en/translation.asp?spen=tacha

(In the Wordreference dictionary, please see what comes under "tacha, borla, cremallera" = studs)