Your search for "Diagonal box" revealed the following:

Diagonal crossing (large) : YSK Unpainted kit N (1:150) Part No. 409

Pull Tab and Violet: Art Stage K - Diorama Art Work Non-Scale

Diagonal Crossing (small) : YSK Unpainted kit N (1:150) Part No. 408

Kakukaku Rail for Mini Mini Train Compatible with Daiso Case (20x10cm) : Yoshiaki Ishikawa Railroad Track 9mm Gauge N(1:150)

Hexagon Socket Head Fittings, Double Dia. 1.8mm Flat, Tapered : Sakatsu Detail Up Non-scale 4458

Hexagon bolt: nut 1.0mm flat diameter : Sakatsuo Detail up Non-scale 4501

Hexagon Socket Head Fittings, Flat 1.5mm Dia. with Taper : Sakatsu Detail Up Non-scale 4461

Hexagonal pipe joint, double flat 1.5mm : Sakatsu Detail Up Non-scale 4452

Hexagon Socket Head Fittings Double 1.5mm dia. with Taper : Sakatsu Detail Up Non-scale 4460

Hexagon bolt 0.9mm flat diameter : Sakatsu Detail up Non-scale 4495

Hexagon bolt: Nut 0.9mm flat diameter : Sakatsu Detail up Non-scale 4496

Hexagonal bolt: nut 0.8mm flat diameter : Sakatsuo Detailing Non-scale 4491

Hexagon joint, flat diameter 0.6mm (for 0.25mm wire) : Sakatsuu Detail Up Non-scale 4470

Hexagon joint, flat 1.5mm: Sakatsu, detail up, non-scale 4453

Hexagon bolt, flat diameter 1.0mm : Sakatsu Detailing Non-scale 4500

Hexagon bolt 0.8mm flat diameter : Sakatsu Detail up Non-scale 4490

Hexagon Socket Head Fittings Double 1.2mm Flat, Tapered : Sakatsu Detail Up Non-scale 4462

Hexagon socket head fitting, flat 1.2mm : Sakatsu Detail Up Non-scale 4455

Hexagon Socket Head Fittings, Flat 1.8mm : Sakatsu Detail Up Non-scale 4451