Introduction
On a Spitzer SF or SK silo trailer, the top fill hatch is the access point through which the tank is loaded with PE/PP granulate or other bulk material. After loading, each hatch must be sealed tight — and that seal is achieved by the wing-nut bolts: simple eye-bolt fasteners that can be tightened by hand, without tools, pressing the hatch cover against its seal. Their condition directly determines the integrity of the top hatch, and therefore the working pressure during pneumatic-aeration discharge and the cleanliness of the transported cargo.
Wing-nut bolts work in harsh conditions: they are permanently exposed to the elements, tightened and released at every loading cycle, and subject to dust contamination and corrosion. Over time the thread, the eye and the zinc coating all wear out. PHS Magnum maintains a stock of complete top hatch bolt assemblies at its warehouse in Chorula near Opole, covering Spitzer, Feldbinder and Kässbohrer trailers — so the right set for a specific hatch can be selected and dispatched without waiting for overseas supply.
Specification and Materials
We supply complete top hatch bolt assemblies (wing-nut bolts) matched to Spitzer, Feldbinder and Kässbohrer silo trailers, along with supplementary fastening hardware.
| Component | Material | Key dimension |
|---|---|---|
| Complete wing-nut bolt assembly | Galvanised steel | 18 mm bolt eye |
| Eye bolt for wing-nut assemblies | Stainless or galvanised steel | All sizes |
| Retaining clip | Brass | — |
Galvanised steel is the standard material for wing-nut bolt assemblies — it combines corrosion resistance with low running costs for a component that is replaced frequently. Eye bolts are available in two material variants: galvanised steel and stainless steel, the latter chosen where enhanced corrosion resistance is important. Brass retaining clips serve as locking elements that hold the assembly in the correct working position.
Sizes and Types
The top hatch bolt range covers the full M20 thread size spectrum, with variants assigned to specific silo trailer makes. All complete wing-nut bolt assemblies have an 18 mm eye.
| Size | Makes | Material | Eye |
|---|---|---|---|
| M20x100 | Feldbinder, Spitzer | Galvanised steel | 18 mm |
| M20x120 | Feldbinder, Spitzer | Galvanised steel | 18 mm |
| M20x130 | Feldbinder, Spitzer | Galvanised steel | 18 mm |
| M20x140 | Kässbohrer | Galvanised steel | 18 mm |
The common denominator across all sizes is the M20 thread and 18 mm eye — meaning the differences come down primarily to shank length, matched to the clamping pack thickness of a given hatch. For Spitzer and Feldbinder trailers the typical sizes run from M20x100 to M20x130; the longer M20x140 is specific to Kässbohrer. The range is complemented by eye bolts for the above wing-nut sets in all sizes (stainless or galvanised steel) and brass retaining clips.
Compatibility with Spitzer Silo Trailers (SF/SK)
The top hatch bolts in our range are assigned directly to Spitzer, Feldbinder and Kässbohrer — these are not generic substitutes of uncertain origin, but components that correspond to the actual hatches produced by those manufacturers. Spitzer SF and SK series silo trailers use M20 wing-nut bolts with an 18 mm eye for their top fill hatches; we hold sizes M20x100 and M20x120 for these in stock.
Because PHS Magnum services both Spitzer trailers and closely related Feldbinder designs within the same fleet operations, we select complete wing-nut hardware with reference to the actual hatch in question, not solely the size designation. When ordering, the key information is the trailer make (Spitzer, Feldbinder, Kässbohrer) and the bolt length (M20x100, M20x120, M20x130 or M20x140) — these two parameters determine the correct fit.
Common Failure Modes
In everyday service practice, top hatch wing-nut bolts wear out faster than most other hardware components, because they are operated at every single loading cycle. Typical signs indicating that a bolt assembly needs replacing include:
- Corroded or damaged eye — makes hand-tightening difficult and risks fracture when pressing the hatch cover down.
- Worn M20 thread — the bolt “slips” or fails to hold clamping pressure, preventing the hatch from sealing properly.
- Damaged zinc coating — exposed steel accelerates corrosion and leads to thread seizure.
- Lost or deformed retaining clip — the assembly loses its lock in the working position.
In each of these cases, the solution is replacement with a complete wing-nut bolt assembly in the correct size, together with a new eye bolt and brass retaining clip where required. When replacing hatch bolts it is also worth checking the condition of the top hatch seal — both components work together to maintain hatch integrity.
Availability and Delivery
Standard top hatch bolt sizes — M20x100, M20x120, M20x130 (Feldbinder, Spitzer) and M20x140 (Kässbohrer) — in galvanised steel with an 18 mm eye are held in stock at our warehouse in Chorula near Opole. Eye bolts in all sizes (stainless or galvanised steel) and brass retaining clips are also in stock. We dispatch by courier throughout Poland and to DACH countries (Germany, Austria, Switzerland).
To select the correct assembly, please provide the trailer make (Spitzer, Feldbinder, Kässbohrer) and the bolt length. For details and an individual quote, ask for a quote.
Related Categories
- Top Hatch Bolts — M20 wing-nut bolts for filling hatch of Spitzer, Feldbinder and Kässbohrer silo trailers.
- Filling Hatch Gaskets — seals that work in conjunction with the wing-nut bolts to close the top fill hatch.
- Rear Hatch Bolts — universal closing system for the Spitzer-Feldbinder silo trailer rear hatch.
- Rear Hatch Seals — seals for Spitzer, Feldbinder and Kässbohrer silo trailer rear hatches.
- Spare Parts for Cement Tankers — specific parts for cement tanker applications (polyamide pads, EPDM seals, discharge valves).
- Spitzer SF and SK Parts — overview of wear and structural parts for the SF and SK series.
- All Spare Parts — full parts catalogue for silo trailers stocked by PHS Magnum.
- Silo Trailer Service — PHS Magnum — overhauls, collision repairs and specialist silo trailer maintenance.
- pasternak.me — expert resource on trailer service, bulk material transloading and bulk transport.
See also: This category in the full PHS Magnum network catalogue (all makes) →
Author: Aleksy Pasternak — Managing Partner PHS Magnum, 20 years in the industry, ISO 9001:2015 internal auditor (DEKRA).
