Serpentine channel / Microreactor, 20x50µm, 342mm length

When should I use the spacers? The metal strips are used for thin bottom chips and are also part of the holder for resealable flow cell's.
This are currently the following products (list might be incomplete): SKU Description Note 00746 Fluidic Connect Pro for resealable flow cells Normally already pre-assembled  00745 Insert set for resealable flow cells   03133 Thin bottom flow cell    03133-F Thin bottom flow cell - coated   03196 Thin bottom flow cell - 0.5mm   03196-F Thin bottom flow cell - 0.5mm - coated   03164 Thin bottom flow cell - 1.5mm   03164-F Thin bottom flow cell - 1.5mm - coated   FC_R50.332.3_PACK Serpentine channel / Microreactor, 20x50µm, 342mm length   FC_R50.332.3-F Serpentine channel / Microreactor, 20x50µm, 342mm length - Coated   03040 Serpentine channel / Microreactor, 45x140µm, 350mm length   03040 - F 03040Serpentine channel / Microreactor, 45x140µm, 350mm length - coated   FC_X3550CH.3_PACK Cross channel chip - thin bottom   How to apply the spacers? The spacers are placed beneath the top insert, as shown in the picture below. What should I do when I don't have spacers available?
Just contact us to request new spacers.

Wet etched structures are extremely smooth and have a roughness in Angstrom range. The structures are fully optical transparent. 
Large roughness for structures in glass chips is typical observed for structures manufactured by use of laser assisted manufacturing techniques or abrasion-based techniques like powder blasting. Almost all catalogue products from Micronit are manufactured using wet etching to create full transparent channels without substantial roughness.