Head restraints are the one thing on the site where the size is the easy part. There are three different families here and they are sized on three different measurements, and two of them also need matching to how far back you sit.
Work out which family you are buying
That is the first fork in the road. A HANS is a neck measurement and a seating angle. A Simpson Hybrid is a chest measurement and there is no angle to pick. A Schroth SHR Flex is a neck measurement and its low collar is designed to work at any seating angle.
Step one: the measurement
Neck, for a HANS, Stand21, Stilo or Schroth
HANS put it plainly on their own chart: neck size is the starting point. Measure around the fullest part of your neck with the tape semi-taut, the way a shirt collar sits.
The bands overlap on purpose. HANS say so themselves: you may fit several sizes and comfort is the deciding factor. Not every model is offered in every size, so check the size list on the product you are looking at. Schroth run two sizes on the SHR Flex, Medium up to 15.5 inch and Large above, and they say a Large is fine on a smaller neck if you want more room over the collar bone.
Chest, for a Simpson Hybrid
The Hybrid is a different shape entirely. It sits over the shoulders and down the chest rather than resting a collar on your shoulders, so it is sized on your chest. Simpson ask for the measurement taken below the pectoral muscles, in your driving suit. If you have not got the suit yet, add an inch.
Step two: the angle, and this is the one people get wrong
A collar-and-tether device has to match how far back you sit. Get the size right and the angle wrong and it will either push your head forward or lift off your shoulders, and you will feel both within a lap.
The rule, from HANSSit in the car in your normal driving position and measure the angle of your chest away from vertical. If it is 25 degrees or more, you want the 30 degree device. Under 25 degrees, the 20 degree.
In practice almost everything sold here is 20 degree, because most of what our customers drive is saloon, GT, rally or track day based and sits fairly upright. The 30 degree comes into its own in single seaters and prototypes. If you are not sure, take a photo of yourself sat in the car from the side and send it over.
Or sidestep the questionThe Schroth SHR Flex and the whole Simpson Hybrid range are built to work across seating positions, so there is no angle to choose. If you run more than one car, or you are between the two angles, that is a genuine reason to look at those instead.
Step three: posts and tethers
Your helmet needs anchor posts
The device clips to two posts fitted to the shell of your helmet. Where a helmet is sold here as part of a HANS package it already has them. If you are buying the two separately, or fitting a restraint to a helmet you already own, you need a post kit to suit that helmet and we will match it for you.
Two anchor systems
Standard posts use a clip that slides over the post. The M61 quick release system uses a sprung anchor that lets you disconnect the tether without unclipping, which is worth having if you get in and out a lot. Simpson Hybrids are offered with either. They are not interchangeable, so pick one and stick with it across the helmet and the device.
Tether lengths
Tethers set how much your head can move before the device takes up. Standard suits most drivers. A shorter tether pulls the helmet in closer, which some drivers prefer in a tight cockpit, and a longer one gives more head movement, which helps if you are looking a long way round in a rally car.
How it should sit
The collar wants to sit flat on your shoulders with the yoke against your chest and no gap under the back of it. Once the harness is over the top and tightened, the device should not be able to slide sideways. If you can shrug and feel it move independently of you, it is too big. If the collar is standing off your shoulders at the back, the angle is wrong rather than the size.
Wear it over your race suit when you try it, not over a t-shirt. A two or three layer suit and a set of shoulder harness straps change the fit noticeably.
Send us the car as well as the measurementNeck or chest measurement, the car, and the helmet you are using. The angle and the post type matter as much as the size and we would rather sort all three at once. Call 0115 989 3488 or email Sales@GSMPerformance.co.uk.
HANS sizing from the HANS device sizing chart and their published angle guidance. Simpson Hybrid sizing from their published chest chart. Schroth SHR Flex sizing from Schroth. Tether and post options from the products themselves. All checked 2 August 2026. Sizes offered vary by model, so the size list on the product page is the final word.
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