Rolex
Datejust 31 178240-0039— lug 16mm

The Rolex Datejust 31 ref. 178240-0039 has a lug width of 16mm. This measurement should be taken internally between the two lug horns using a digital calliper, positioning the instrument at the narrowest point of the gap. It is essential to respect this exact value when purchasing an aftermarket strap, as even half a millimetre of discrepancy will affect alignment and clasp fit.

For the stainless steel Datejust 31 ref. 178240-0039, a vegetable-tanned alligator strap is the classic choice for formal occasions, offering a regular grain and a patina that develops beautifully with wear. Box-calf leather is an elegant and more accessible alternative. For everyday or sport use, a curved-end vulcanised rubber strap or a two-piece nylon NATO are functional options without aesthetic compromise. A deployant clasp is recommended to reduce wear on the leather at the keeper.

To replace the strap on the Datejust 31, a fine-tipped spring bar tool is required. Insert the tip into the springbar slot laterally at the lug, compress the spring and slide the strap free. Care should be taken to avoid scratching the case: protecting the lugs with low-tack adhesive tape or using a dedicated watch cushion is advisable. The new 16mm strap is fitted by compressing the spring bar in the opposite direction.

Yes, the aftermarket offers straps compatible with the Datejust 31 in 16mm. Artisan manufacturers such as Casati Milano produce straps with straight or shaped ends calibrated to the specific lugs of this model. It is important to verify not only the attachment width (16mm) but also the end shape and thickness, as the Datejust 31's lugs are short and require straps of contained height for a correct fit.

The lifespan of a leather strap depends on material quality, frequency of use and wearing conditions. A high-quality vegetable-tanned alligator strap, rotated with other straps and protected from excessive moisture, can last between 3 and 7 years whilst maintaining structural integrity and a presentable appearance. Shell cordovan typically lasts longer due to the compactness of the fibre. Regular application of leather conditioner and timely replacement of the keeper when it shows signs of wear will significantly extend the strap's service life.