For the difference between 0903WsWl and Initial brush #4, the hairs belong to the same type but different grade. The 0903WsWl has much higher than than the initial brushes. The 0903WsWl is designed to suit for all levels, including levels from beginners to professionals. The initial brushes are designed specifically for beginners. The hair grade of initial brushes is lower and therefore the price is very affordable. 🙂
I hope this answer is helpful! If you still cannot decide and need assistance, please kindly let me know your level and type of painting/ calligraphy you mostly do.
I could tell you that each hair bristle is approximately 0.3m/m with an average ratio broadness of about 0.2-1.03% across the perimeter of the base but……………………….
By the end of understanding the brushes properties you’d be an engineer…. not an artist.
Like Yan explained the brushes are similar but from a different grade. As a beginner you might want to not spend too much money on a brush but still have a decent brush – that’s the Initial #4.
When you are on a level where you want to invest in a good brush, the 0903WsWl brush is a good one.
Compare it with like buying a t-shirt. You need a new tshirt but you decide if you want a good one for a okay price or you want a good (to better one) for a more expensive price. It’s still just a tshirt only the materials and work put into it can differ.