What do the dimensions 17" x 3.5" x 3.5" mean when describing a model rocket? I'm new and have no idea what it means please help.

Welcome to the forums! Where did you get this? We usually describe a model rocket in terms of diameter (main body tube) and overall length. We will also add a 'fin span' (the distance from fin tip to fin tip). In this case, your 'fin span is 3.5" What you have is likely the 'rectangular volume' the rocket takes up; how big a box you would need to package it. In this case, something 17" long x 3.5" high x 3.5" deep..

I see these numbers on loc precision looking at the EZE park flyer on the additional information tab Is it like you said dimater length and fin span

The notes for the rocket say it is 25" tall,1.63" diameter (BT60), and 9 oz. So those numbers that you're seeing really must be shipping weight and dimensions. Bad job by the LOC website.

I just measured the box my LOC Park Flyer Hawk was packaged in: 3.5" x 3.5" x 18", which is quite close to the 3.5" x 3.5" x 17.5" figure stated on: https://locprecision.com/product/pfy-hawk/ The 0.99 lbs weight likely refers to the package as shipped. It's not an exact weight, what matters for shipping is that it's less than 1 lbs. This defines the shipping cost category. My point: the numbers under the "Additional Information" tab refer to the packaged product. You might be able to use them to estimate the shipping cost, but LOC might also package it in a bigger box. The rocket dimensions are in the upper notes: 25" for the EZE (23" for my Hawk). All park flyers are 1.63" in diameter.

I'd like to think they are the dimensions for an (ostrich) egg lofter or tank buster. But that's just me.