Towbar cover: selection, installation, rules
A skull cover for a towbar is a skull cap that you slip over the coupling ball. It keeps dirt, moisture, and grease off the ball and gives the rear of your vehicle a unique look. In Germany, a ball cap is almost always the right choice, not the American receiver cover for a 2-inch tube that you see in many shops. Here you will find out which design fits your towbar, how to mount the cap securely, what rules apply to license plates and lighting, and what to consider when using a trailer.
Important insights
- Ball cap instead of receiver cover: Cars in Germany use a ball coupling with a standardized ball diameter of 50 mm. Many skull products from the USA are designed for a 2-inch receiver tube and do not fit here at all.
- No lights, no reflectors: According to § 49a StVZO, only prescribed and permitted lighting devices are allowed on the vehicle. Glowing skull eyes therefore do not belong on the car.
- Keep license plate clear: If the ball covers the rear license plate, a removable ball must be used. The nicest cap in the world doesn't change that.
- Material matters: Outdoors, UV resistance and heat resistance count. That is why we print our skull cap from PETG.
- Take it off before coupling: The cap is a protective cover for when it is not in use. Remove it before towing and put it in the glove compartment.
Table of contents
- What exactly a skull cover is
- Does the cap fit your towbar?
- Materials and designs of skull covers
- How to properly mount the skull cap
- What is permitted in Germany
- Skull cap and trailer operation
- Our view as geocachers and tinkerers
- The skull cap from CacheWerk
- Frequently asked questions about the skull cover
- Sources
What exactly a skull cover is
Under this term, you will find two completely different products online. If you don't know that, you will quickly order the wrong one.
The ball cap: the standard in Germany
The ball cap sits directly on the coupling ball. It is slipped on, encloses the ball and the upper part of the neck, and can be removed with one hand. It is the usual form with us because almost all cars, vans, and motorhomes are equipped with a ball coupling. Classic protective caps are plain black plastic or rubber covers. A skull cap serves the same purpose, only with a skull design.
The receiver cover: the US standard
In North America, many pickups and SUVs use a square receiver tube, the receiver. The ball mount is inserted into this tube. When no trailer is attached, a hitch cover is inserted, often made of steel or chrome-plated plastic, sometimes even illuminated. These are exactly the products that appear when you search for “skull tow hitch”. For a German car with a ball coupling, they are almost always useless because the appropriate tube simply does not exist.
Why the difference is important
Pay attention to the fitment information when purchasing. If it says “2-inch receiver” or “2" hitch”, a receiver tube is meant. If it says “ball cap”, “towbar cap”, or “for coupling ball”, you are in the right place. An inch measurement on a ball cap is also a warning sign: A 2-inch ball measures around 50.8 mm and is not the same as the European 50 mm ball.
Does the cap fit your towbar?
The good news: On cars, the ball is standardized. The coupling ball has a diameter of 50 mm, regardless of whether it is on a small car, a station wagon, or a camper. A 50 mm ball cap therefore fundamentally fits every car ball. Differences exist in the neck under the ball and in the design of the coupling.
The three designs at a glance
| Design | How it works | What this means for the cap |
|---|---|---|
| Fixed coupling | The ball neck is firmly screwed on and always remains on the car | The cap is permanently in use and protects the ball every day |
| Removable coupling | The ball neck is inserted when needed, vertically, diagonally, or horizontally | The cap protects the ball while the neck is mounted, and in the trunk from dirt on other luggage |
| Swivel coupling | The ball neck folds behind the bumper | The cap is removed before swiveling so that nothing gets stuck |
Quick fitment check
- Look at the ball: Is it clean and round? Remove coarse dirt and old grease beforehand.
- Check the neck: Some ball necks have a wide collar or a socket holder directly under the ball. The cap must be able to slide down to the neck base.
- Check the clearance: With swivel systems, you check whether the cap obstructs the swivel path.
- Test the fit: The cap should sit firmly without being pressed on with force.
Materials and designs of skull covers
The skull look is available on many materials. For everyday use in Germany with rain, road salt, frost, and summer sun on the asphalt, the material plays the main role.
| Variant | Typical material | Use in Germany |
|---|---|---|
| Skull ball cap, 3D-printed | PETG or similar engineering plastics | Fits the 50 mm ball, individually customizable, weatherproof with the right material |
| Simple protective cap | Rubber or soft plastic | Functional, but without design |
| Metal emblem cover | Steel, aluminum, often powder-coated | Mostly for 2-inch receivers, rarely usable on German cars |
| Illuminated skull cover | Chrome-plated plastic with LED | Unsuitable for road use here, see rules below |
Why the printing material counts
The towbar cap is constantly exposed to the weather. In summer, the rear heats up strongly in the blazing sun, in winter frost and salt water are added. A material that becomes soft or brittle here will not last long. PETG is popular for exactly such outdoor uses because it is robust and weather-resistant. How we use PETG for our geocache hides and what matters when printing, we show in the PETG guide for 3D printing. The experiences from the field are also in our skull cap.
Design variants
With the skull itself, you have free choice: grim, playful in the sugar skull style, minimalist, or with details like teeth and eye sockets. The only important thing is that the design has no sharp points facing outward. When maneuvering in the parking lot or loading the trunk, you often stand directly next to the coupling.
How to properly mount the skull cap
The mounting takes no more than a minute. With these steps, the cap sits securely and lasts a long time.
- Clean the ball: Wipe off dust, sand, and old grease with a cloth. Dirt under the cap acts like sandpaper.
- Align: Turn the skull so that the face looks backward. That is the look that the driver behind you sees.
- Place on: Place the cap straight on the ball and push it down with even pressure.
- Check the fit: Shake the cap briefly. It should not wobble and not slide off on its own.
- Check the license plate: Take a few steps back and see whether the license plate, taillights, and rear fog light remain clearly visible.
Theft protection in everyday life
A cap placed on top can naturally be removed by others as well. With a few habits, your skull will still stay where it belongs:
- Removable ball neck: Remove the neck with the cap when you park for a longer time, for example at the train station or at the festival parking lot. The neck and cap then lie safely in the trunk.
- Fixed coupling: A tight, firm fit makes it harder to pull off in passing.
- Park well visible: In busy corners, hardly anyone is interested in your rear.
Durability and care
Rinse the cap with clear water after winter drives so that no salt settles. Take it off now and then and let the ball and cap dry so that no moisture accumulates. You do not need aggressive cleaners and solvents, a damp cloth is enough.
What is permitted in Germany
The cap itself is an accessory for the ball. Nevertheless, there are two points where it comes into contact with regulations: visibility of the license plate and lighting.
License plate must remain clear
The coupling ball must not cover the rear license plate. If this is the case, according to the EC directive 94/20/EC, a ball removable without special tools must be used. This is stated, for example, in the installation instructions of the vehicle manufacturers. For you, this means: On some cars, the license plate sits deep in the bumper. If the ball neck takes away the visibility there, the neck must be removed during drives without a trailer. The cap does not change this obligation, but it must not exacerbate the problem either. Therefore, choose a cap that is not significantly wider or higher than the ball itself.
Stay away from lights and reflectors
Many US skull covers have glowing eyes or brake light functions. In Germany, this is a problem. According to § 49a StVZO, only the prescribed and declared lighting devices may be attached to motor vehicles. Luminous substances and retroreflective means are also considered lighting devices there. An LED in the skull or glued-on reflector eyes are therefore not a good idea. A cap without light and without reflective material is, on the other hand, simply a piece of plastic on the ball.
If you are unsure
If you have doubts whether your setup is okay, for example with a low-sitting license plate or a retrofitted coupling, ask the inspector from TÜV, DEKRA, or GTÜ at the next general inspection or your specialist workshop. They know your coupling and your entry in the documents.
Skull cap and trailer operation
The cap is intended for the time when no trailer is attached. As soon as you couple up, it takes a break.
Before coupling up
- Remove the cap and store it in a fixed place, for example in the glove compartment or in the door pocket. This way you will find it immediately after the drive.
- Check the ball: Is it clean and undamaged? Sand or little stones from the parking lot do not belong between the ball and the coupling mouth.
- Observe the manufacturer's specifications: Some towbars, for example with a stabilization system, place their own requirements on the ball surface. Stick to the operating instructions of your trailer.
- Couple up as usual: Place the coupling on, check the locking, attach the safety cable, plug in the connector, test the lighting.
After uncoupling
Close the socket, wipe the ball briefly, put the cap back on. It takes no more than ten seconds and protects pants and shopping bags from grease stains when you walk past the rear.
Planning your own trailer?
Who is just starting with towing often buys their own trailer for bicycles, garden waste, or the camping equipment right away. It needs its own registration and its own license plate in Germany. What documents you need for this and what the process looks like, you can find in the guide Registering a trailer: Documents and process.
Our view as geocachers and tinkerers
At CacheWerk, we have been printing hides for years that have to withstand the outdoors: on guardrails, in hedges, on lampposts. A hide that becomes soft after the first summer or gets cracks in winter is removed from our range. Exactly with this standard we approached our skull cap for the towbar.
The towbar is a pretty tough workplace for a piece of plastic. Spray water from the road, road salt, heat from the asphalt, and occasionally a bump when loading. That is why we rely on PETG. We also work with this material for our cache hides, and it has proven itself in outdoor use.
It is also important to us that the cap fits German cars. Many skull covers that you find online are made for American receiver tubes or have built-in lights. Our cap is intended for the ball, without electronics and without gimmicks that could cause you trouble on the road.
And yes: A little fun is part of it. Those who buy hides from us love to add a touch of humor to everyday things. A skull on the towbar is exactly the kind of detail that gets people talking in the parking lot.
Benedikt
The Skull Cap by CacheWerk
Do you want to add a skull to your towbar that fits German couplings and can withstand the elements? Our PETG Skull Towbar Cap is 3D printed and was developed by active geocachers who know what the weather does to plastic.
Do you prefer tinkering yourself and have your own printer? Then check out our 3D printing files category. And if you want more after the towbar cap, check out the Camping, Car and Family section by ABCreative for more thoughtfully designed accessories for on the go.
Frequently Asked Questions About the Skull Cap
Will a 2-inch skull cap fit my towbar?
In most cases, no. Products labeled “2 inch” are usually designed for an American receiver tube, which is rarely found on German passenger cars. For a ball coupling, you need a cap for the standardized 50 mm ball.
Can I drive normally with the skull cap on?
A cap without lights or reflectors is simply a cover for the ball. The important thing is that the license plate and lights remain clearly visible. If the ball obscures the license plate, it must be removed when driving without a trailer, with or without the cap.
Does the cap have to be removed when towing a trailer?
Yes. The ball must be freely accessible in the trailer's coupling socket. Remove the cap before coupling, store it in the car, and put it back on after uncoupling.
Why is PETG better than just any 3D printing plastic?
The coupling is directly exposed to the sun, heat, frost, and salt. PETG is robust and weather-resistant, making it suitable for outdoor use. We also use it for our geocache hides.
How do I clean the skull cap?
Remove it, rinse it with clean water, and let it dry. This is especially worthwhile after winter driving to prevent road salt from getting stuck in the details. A damp cloth is perfectly sufficient; you don't need harsh cleaners.
Sources
- Towbar coupling, Wikipedia
- BMW parts and accessories, towbar installation instructions (EC Directive 94/20/EC)
- § 49a StVZO, lighting equipment, LexMea