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MB&F · Horological Machines

Strap for Horological Machine N°4 HM4 Thunderbolt Yellow Gold

Takes 20 mm straps. Verified lug width, the straps that fit this model, and answers to the most common questions.

Lug width

20mm
20 mm strapsAll MB&F
Lug width20 mm
Case diameter54 mm
Reference40.TSYL
FamilyHorological Machines
MovementMB&F caliber HM4 hours, minutes | power reserve indicator
Year2014 - 2014
CaseTitanium, Yellow Gold, Sapphire

Spring bar

Swiss Standard universal spring bars

The right category for this model · 316L steel, all lug widths 13–26 mm

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Straps for the Horological Machines 40.TSYL

Selected for the 20 mm lug width · workshop selection

All 20 mm straps →

The Horological Machines 40.TSYL, seen from the bench

The Horological Machine HM4 represents one of MB&F's most distinctive creations in the field of contemporary horology. It is equipped with the MB&F HM4 caliber with indication of hours, minutes and power reserve. The 40.TSYL reference features a three-dimensional design that reinterprets the traditional time display.

Frequently asked questions

What is the lug width of the MB&F Horological Machines 40.TSYL?

The MB&F Horological Machines 40.TSYL features a lug width of 20 millimetres. This measurement is crucial for strap compatibility: it is taken from the base of one lug to the other at the attachment point to the case. Only straps with a 20mm lug width will fit correctly on this model.

Which type of strap is best suited for the MB&F Horological Machines 40.TSYL?

Given the experimental architecture and monumental proportions of the case, premium alligator straps are recommended for a refined aesthetic, or vegetable-tanned calf leather for a more contemporary character. Technical NATO straps in dark tones amplify the aeronautical DNA of the design, whilst rubber represents the most radical choice for a sporty, functional look. The material should be selected in harmony with the watch's aesthetic vocation.

How do I change the strap on an MB&F Horological Machines 40.TSYL?

The 40.TSYL strap is replaced by removing the fixing pins (lugs) that connect the strap to the case edges. Using a strap removal tool or fine needle, position the pin vertically and push gently until it releases. Once removed, align the new strap holes with the lugs and reinsert the pin until it clicks into position. Proceed with care to avoid scratching the titanium and gold case.

Can I use third-party aftermarket straps on my 40.TSYL?

Yes, provided the aftermarket strap has a 20-millimetre lug width. Milano Straps offers a comprehensive collection of artisanal, compatible straps constructed from premium materials—alligator, calf leather, technical NATO, and rubber—precisely sized for the 40.TSYL. Selecting a high-quality aftermarket strap allows you to personalise the watch whilst maintaining elevated construction standards.

How long does a leather strap last on a watch of this magnitude?

A premium, handcrafted leather strap has a lifespan of 2-4 years under normal use conditions, considering the weight and monumental dimensions of the 40.TSYL case (54mm diameter and beyond). Vegetable-tanned straps tend to age elegantly, developing natural patina, whilst alligator maintains extended durability owing to skin density. Factors such as humidity, frequency of wear and maintenance significantly influence longevity. Rubber and NATO straps have longer lifespans, reaching 5-8 years with proper care.

The next step

The right strap isn't chosen. It is built, together.

From the atelier appointment to delivery, every step is made for those who know that things done well take time. Rare leathers, one piece at a time, eighteen months of warranty.

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Casati Milano · Via XX Settembre 15, Milan · by appointment only