25 vehicles built by ...... you know
(again Jugoslavian FABRYKA SINSKIH VOZILA SUBOTICA, BRATSTVO - JUGOSLAVIJA, 1967)
series ΧΤΣΠ / Ι17 86001-86025 ... which (to be precise) are ballast cars

(that's why they are Χ, from ΧΟΑΝΗ)
Some of them were improved .... with new χοάνες for letting the ballast out from the sides, with those large triangles and grey colour.
86013 - Kalamata
86022 - Lechena