Tri-clamp diaphragm centre disc and backing disc: 1.5 and 2 in — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/tri-clamp-diaphragm-disc/  (CC BY 4.0)
Basis: Design values: disc diameter chosen so the free membrane span gives the design stroke; M2 screws (ISO 4762) and ISO 273 medium clearance holes
Catalog version: 2026-10-20

Sizes: see table below
- The centre disc sits on the head side of the membrane and carries the rod: a Ø8 × 8 boss with a Ø3 socket (floor 1 mm above the membrane side) held by an M3 grub in a Ø2.5 radial hole 4 mm up the boss. The backing disc sits on the gas side.
- Three M2 × 8 screws go from the gas side through the backing disc, the membrane and the centre disc into M2 nuts on top; the nuts sit flat-side to the boss.
- Disc Ø17 (1.5 in) and Ø20 (2 in): smaller discs leave more free span, so more stroke at the same membrane stretch.

size_in  disc_dia_mm  disc_t_mm  backing_t_mm  boss_dia_mm  boss_h_mm  screw_circle_mm  screws
2  20.0  3.0  2.0  8.0  8.0  13.0  3 × M2 × 8 + nuts
1.5  17.0  3.0  2.0  8.0  8.0  12.0  3 × M2 × 8 + nuts

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- ISO: ISO 273 clearance holes for bolts and screws (fine / medium / coarse) — standard — dimensions are facts [verify license at link] — https://www.iso.org/standard/4196.html
- Long Earth Society: Engine builds — web, video — LES site — https://longearthsociety.com/engineering/

Free files (CC BY 4.0, Xem Studio; STEP + STL, 4 parts): https://xemstudio.com/files/hardware/tri-clamp-diaphragm-disc/index.json
API: https://xemstudio.com/api/geometry?object=tri-clamp-diaphragm-disc