This paper presents a study on how to calculate the net-tension failure resistance of steel bolted connections of fibre-polymer composites, focusing on the challenges of determining the stress concentration factor for the 4 × 4 bolting configuration. The research addresses the need for a reliable resistance formula in terms of wanting to establish the stress concentration factors for distinct bolted connections configurations using a semi-empirical approach (with details in accordance with the CEN European Technical Specification CEN/TS 19101:2022). The study, therefore, employs a combination of experimental testing and analytical modelling. Bolted connections and coupon specimens were fabricated using pultruded flat sheet material and precision CNC machining. Both batches of five specimens were tested under tensile load. Test results for the 4 × 4 configuration show that the net-tension failure mode occurs at the first row of bolts. Using mean values and the CEN/TS 19101:2022 resistance formula (in sub-clause 12.3.2.1), the stress concentration factor is 1.3. This finding strengthens and can expand the applicability of bolted connections configurations permitted using CEN/TS 19101:2022. This new contribution to understanding, therefore, advances the design options for bolted connections of fibre-polymer composites and can contribute to the ongoing standardization of design procedures under the Eurocode framework.