DIN 1480 and DIN 1478 specify the dimensions and the thread form of the turnbuckle. They do not specify a working load limit. Load figures in suppliers' catalogues are each manufacturer's own declared values, not a standard figure.
To give you a sense of the range: published catalogues for DIN 1480 eye-and-eye turnbuckles in carbon steel list roughly 230 kg at M6 rising to about 9,300 kg at M36. Two independent sources differ by around 2–3% at the same size, which is why we quote a range rather than a single number.
The rated figure depends on the end fittings (eye, hook, jaw, stub end), the material and the heat treatment — so two turnbuckles of the same thread size can legitimately carry different ratings.
Caution:Turnbuckles are tensioning devices, not lifting devices. Every catalogue we checked states this without exception: turnbuckles must never be used for lifting. Use them for tensioning, bracing and adjustment only.
Sources: Eurocable (NL) DIN 1480 eye/eye and eye/hook listings; CLGR Industrial DIN 1480 stub end; Seriga Lifting DIN 1480; Deyuan Marine DIN 1480. Figures cross-checked across these four — the two clusters of values differ by 2–3%.