Weibull weakest link model has been widely applied for the fracture probability scaling of brittle materials. However, a discrepancy has been reported on some brittle monofilaments between the estimated fracture probability and the derived data in the way as if the Weibull parameters were dependent on the gauge length. This paper discusses an interpretation of flaw size distribution for Weibull parameters on the strength size-effect of brittle monofilaments. A model on monofilament strength size-effect was firstly presented through coupling a Griffiths fracture mechanics and a distribution of crack initiating flaw size. The model parameters and Weibull parameters were secondly compared to provide a relationship between Weibull parameters and flaw size distribution. The results have read to a mathematical model of Weibull parameter dependence on the monofilament gauge length. The standard deviation of the flaw size distribution was found in the model an important factor of the gauge length dependence. Then thirdly the mathematical model was applied on the Weibull parameters of Tyranno ZMI Si-Zr-C-O monofilament strength to assess if real monofilament reveals through the modeling the parameter dependence on the gauge length. The result have indicated that the effectiveness of Weibull scaling might be questioned due to the variable Weibull parameters for the case to scale the fiber strength of 'pull-out length' level gauge using the data of rather long samples for monofilament tensile test.