The quickest and easiest way to see if a product/part will fit your car is to use the parts finder where you can easily Shop by model.Shop by model
The other way is to find the SKU (part number) in your model's manual. Most RC cars even come with an exploded view which will make locating the correct part number easy.
Besides reading the products title for your model the only other way (unless you can tell purely from the image) is
by measuring parts.
This is sometimes impossible for some parts (like suspension arms and hubs) but can be very easy for parts like:
If you've tried all methods above and you're still scratching your head, then it might be time to contact the experts. If you do, please be ready with all the information you already know like SKU, brand, model and if you don't know any of them, make sure you send a picture of the part you need and the car you have.
There are various sizes & specs listed under the specifications tab on the product's page.
If the specific size or measurement you're looking for isn't there then press the "Request Info" button on the product page (located just under the add to cart button) and we'll get it for you.
The kg rating is how much weight the servo can pull up vertically when attached 1cm out from the centre of the servo's spline.
For example, if we have 10kg servo, and install the linkage only 0.5cm from the centre of the spline then the servo can actually pull/push 20kg for the same reason it's easier to remove a bolt with a long spanner than a short one.