| Description | Date | Identifier | |
| Letter from Zenith Carburetter Co. Ltd. discussing filter modifications, using duralumin and increasing the number of discs. | 8th Jun 1927 | Box 44 \ 1 Scan157 | |
| Letter from The Zenith Carburetter Co. regarding tests and the standardisation of a filter. | 8th Jun 1927 | Box 44 \ 1 Scan158 | |
| Letter to Zenith Carburetter Co. regarding proposed design modifications to a filter element and requesting samples for testing. | 9th Jun 1927 | Box 44 \ 1 Scan159 | |
| Letter from Zenith Carburetter Co. Ltd. regarding modifications to a petrol filter. | 10th Jun 1927 | Box 44 \ 1 Scan160 | |
| Standardisation report for a Zenith petrol filter to prevent jet stoppage. | 23th May 1927 | Box 44 \ 1 Scan161 | |
| Introduction of a new standardized chassis part. | 8th Oct 1927 | Box 44 \ 1 Scan162 | |
| Letter from The Zenith Carburetter Co. Ltd. discussing modifications and material challenges for two sample petrol filters. | 4th Jul 1927 | Box 44 \ 1 Scan163 | |
| Page two of a letter from The Zenith Carburetter Co. Ltd. awaiting a report on good qualities. | 4th Jul 1927 | Box 44 \ 1 Scan164 | |
| Introduction of a new type of petrol filter and the cancellation of the existing ones in the carburettor float chambers. | 20th Jul 1927 | Box 44 \ 1 Scan165 | |
| Letter from Zenith Carburetter Co. Ltd. requesting a test report on sample filters and 42 HK carburetters. | 26th Jul 1922 | Box 44 \ 1 Scan166 | |
| Modified Zenith petrol filter, its production status, weight, and potential material changes. | 10th Aug 1927 | Box 44 \ 1 Scan167 | |
| Test report on the Hele-Shaw filter detailing its failure due to choking and bursting, with a recommendation for a relief valve. | 3rd Oct 1927 | Box 44 \ 1 Scan168 | |
| Letter discussing the material composition and properties of a felt filter for use in a carburettor. | 27th Oct 1927 | Box 44 \ 1 Scan169 | |
| Felt petrol filter as a solution for carburettor jet stoppage on the 20 HP model. | 2nd Nov 1927 | Box 44 \ 1 Scan170 | |
| Ionides petrol filter sent to stores for examination. | 3rd Nov 1927 | Box 44 \ 1 Scan171 | |
| Comparing the performance of the Ionides and Zenith type petrol filters. | 3rd Nov 1927 | Box 44 \ 1 Scan172 | |
| Inquiry regarding experience with 'Auto-Clean' and 'Cuno' cleanable disc filters. | 7th Nov 1927 | Box 44 \ 1 Scan173 | |
| Letter from Zenith Carburetter Co. Ltd. about invoicing for 10 sample filters. | 15th Nov 1927 | Box 44 \ 1 Scan174 | |
| Notification regarding a blueprint for the Zenith Filter and Piping on the Phantom Chassis. | 19th Nov 1927 | Box 44 \ 1 Scan175 | |
| Requesting blueprints and the production of a Zenith Filter and associated parts for an experimental Phantom Chassis. | 23th Nov 1927 | Box 44 \ 1 Scan176 | |
| Letter from the American office to Derby discussing the performance of Cuno, Purolator and Auto-Clean oil filters. | 23th Nov 1927 | Box 44 \ 1 Scan177 | |
| The trial of Auto-Clean strainers for both oil and petrol. | 6th Dec 1927 | Box 44 \ 1 Scan178 | |
| Order of K-S Telegage liquid Capsules from Messrs. Hobson. | 7th Jan 1928 | Box 44 \ 1 Scan179 | |
| Alternative petrol filters and pipes for the 20-HP chassis. | 13th Jan 1928 | Box 44 \ 1 Scan180 | |
| Extract from a letter by Messrs Benton & Stone Ltd. detailing the features and benefits of their solderless unions and patent pipe nipples. | 6th Jan 1928 | Box 44 \ 1 Scan181 | |
| The examination of a Benton & Stone filter and a request for modifications. | 14th Jan 1928 | Box 44 \ 1 Scan182 | |
| From Hs/Rn to Roy stating a preference for a glass container in reference to a letter from Messrs. Benton & Stone. | 23th Jan 1928 | Box 44 \ 1 Scan183 | |
| 20-HP chassis petrol filter, comparing a sample from Benton & Stone with the existing Zenith filter. | 24th Jan 1928 | Box 44 \ 1 Scan184 | |
| The delivery of a revised Enots petrol filter, with a handwritten reply. | 2nd Feb 1928 | Box 44 \ 1 Scan185 | |
| Proposal to incorporate a petrol filter due to contaminants found in fuel dispensed from Bowser tanks. | 1st Feb 1928 | Box 44 \ 1 Scan186 | |
| Letter from Auto Klean Strainers Ltd requesting a report on a supplied lubricating strainer and confirmation of retention for invoicing. | 27th Feb 1928 | Box 44 \ 1 Scan187 | |
| Letter from Benton & Stone Ltd. concerning modifications to an 'Enots' Visible Petrol Filter. | 28th Feb 1928 | Box 44 \ 1 Scan188 | |
| Correspondence concerning the Benton & Stone petrol filter, its cost-effectiveness, and potential use on new 20 HP and 40/50 HP chassis. | 29th Feb 1928 | Box 44 \ 1 Scan189 | |
| Instructing stores to return a Benton & Stone petrol filter to the manufacturer for a modified version. | 2nd Mar 1928 | Box 44 \ 1 Scan190 | |
| Letter to AutoKlean Strainers Ltd. expressing satisfaction with an oil filter after a 6-month test and requesting a quotation. | 6th Mar 1928 | Box 44 \ 1 Scan191 | |
| Request to place an official order for an Auto Klean Filter following a successful six-month test period. | 14th Mar 1928 | Box 44 \ 1 Scan192 | |
| Request to add a note to the instruction book about cleaning the Zenith Petrol Filter every 2000 miles. | 1st May 1923 | Box 44 \ 1 Scan193 | |
| Letter to Benton & Stone Ltd. regarding the development and testing of a Zenith petrol filter. | 16th May 1928 | Box 44 \ 1 Scan194 | |
| The advantages of the Zenith filter, which has been standardised on the 20 HP model. | 17th May 1928 | Box 44 \ 1 Scan195 | |
| Letter from Benton & Stone Ltd. regarding experiments to develop a Petrol Filter based on an interview and blueprints provided. | 17th May 1928 | Box 44 \ 1 Scan196 | |
| Letter from Zenith Carburetter Co. Ltd. regarding complaints of breakages on glass petrol filters. | 17th May 1928 | Box 44 \ 1 Scan197 | |
| Letter from Zenith Carburetter Co. discussing the issue of bursting glass bowls and potential solutions. | 17th May 1928 | Box 44 \ 1 Scan198 | |
| Letter from Zenith Carburetter Co. regarding failures of glass bowls and the introduction of a new 'hard flint' glass. | 17th May 1928 | Box 44 \ 1 Scan199 | |
| Letter from Zenith Carburetter Co. regarding the supply of glass bowls and an offer to exchange them for brass bowls. | 17th May 1928 | Box 44 \ 1 Scan200 | |
| Standardisation of chassis parts, specifically the Zenith Filter. | 23th Mar 1928 | Box 44 \ 1 Scan201 | |
| Standardisation document for a new chassis part detailing the first chassis fitment, test date and costs. | 12th Nov 1928 | Box 44 \ 1 Scan202 | |
| The breakage of Zenith petrol filter glasses, finding the response unsatisfactory and suggesting a switch to metal containers. | 21th May 1928 | Box 44 \ 1 Scan203 | |
| Experimental order request for a Zenith Petrol Filter with a metal cover and two spare metal covers. | 23th May 1928 | Box 44 \ 1 Scan204 | |
| Letter from Zenith Carburetter Co. regarding a defect in their petrol filters. | 2nd Jun 1928 | Box 44 \ 1 Scan205 | |
| Works complaint about Zenith petrol filters where the glass container does not fit correctly. | 4th Jun 1928 | Box 44 \ 1 Scan206 | |
| Faults with Zenith Petrol Filters, including tight-fitting glasses and non-concentric stirrups. | 5th Jun 1928 | Box 44 \ 1 Scan207 | |
| Confirming a previous communication about an incorrect charge for six filters from Zenith Carburetter Co. Ltd. | 11th Jun 1928 | Box 44 \ 1 Scan208 | |
| Confirming that payment is required for filters as no agreement for free supply was found. | 6th Jun 1928 | Box 44 \ 1 Scan209 | |
| Issues with cracked and chipped glasses on Zenith Petrol Filters due to being too tight in the housing. | 13th Jun 1928 | Box 44 \ 1 Scan210 | |
| Purchase of two Zenith petrol filters and the subsequent invoice. | 21th Jun 1928 | Box 44 \ 1 Scan211 | |
| Blueprint for a flexible magneto drive for the F Type Engine. | 22th Jun 1928 | Box 44 \ 1 Scan212 | |
| Returning an Enots petrol filter to its makers for examination during a redesign. | 25th Jun 1928 | Box 44 \ 1 Scan213 | |
| The failure and subsequent modification of an Enots petrol filter fitted to car 12-EX. | 25th Jun 1928 | Box 44 \ 1 Scan214 | |
| Two broken Zenith petrol filter tumblers found on new 20-HP chassis. | 29th Jun 1928 | Box 44 \ 1 Scan215 | |
| Broken Zenith petrol filter glass bowls, identifying causes and proposing the temporary use of metal bowls during testing. | 1st Jul 1928 | Box 44 \ 1 Scan216 | |
| Return of two cracked and ill-fitting Zenith filter glasses. | 10th Jul 1928 | Box 44 \ 1 Scan217 | |
| Cracked Zenith petrol filter glasses and arranging their replacement and return. | 11th Jul 1928 | Box 44 \ 1 Scan218 | |
| Complaints from the Sales Department about broken Zenith petrol filters. | 6th Aug 1928 | Box 44 \ 1 Scan219 | |
| Fractures and internal stress cracks in Zenith petrol filters. | 20th Aug 1928 | Box 44 \ 1 Scan220 | |
| Requesting the return of three defective Zenith Petrol Filter Tumblers to the manufacturer for replacement. | 23th Aug 1928 | Box 44 \ 1 Scan221 | |
| Letter to The Zenith Carb. Co. Ltd. regarding defective petrol filter tumblers and requesting a meeting. | 23th Aug 1928 | Box 44 \ 1 Scan222 | |
| Letter from Zenith Carburetter Co. Ltd. regarding the return of broken Pyrex Glass Filter Bowls. | 27th Aug 1928 | Box 44 \ 1 Scan223 | |
| Feedback on an experimental petrol filter, suggesting design modifications to improve petrol flow. | 27th Aug 1928 | Box 44 \ 1 Scan224 | |
| Letter from Benton & Stone Ltd regarding modifications and samples of an improved petrol filter. | 30th Aug 1928 | Box 44 \ 1 Scan225 | |
| Letter to Messrs. Penton & Stone discussing filter modifications, including the use of a duralumin bowl to prevent breakage. | 31th Aug 1928 | Box 44 \ 1 Scan226 | |
| Letter from a supplier discussing the manufacturing process for a duralumin bowl for special petrol filters. | 3rd Sep 1928 | Box 44 \ 1 Scan227 | |
| Letter from Zenith Carburetter Co. Ltd. regarding the supply of new flint glasses for petrol filters. | 4th Sep 1928 | Box 44 \ 1 Scan228 | |
| Letter from The Zenith Carburetter Co. regarding patented filtering elements, page 2. | 4th Sep 1928 | Box 44 \ 1 Scan229 | |
| Blueprint of an oil filter assembly. | 16th Aug 1928 | Box 44 \ 1 Scan230 | |
| Very faint blueprint of a component, stamped by Zenith Carburetter Co. Ltd. | 4th Sep 1928 | Box 44 \ 1 Scan231 | |
| Letter from Benton & Stone enclosing a sample of an aluminium sump for a petrol filter for approval. | 12th Sep 1928 | Box 44 \ 1 Scan232 | |
| Correspondence providing feedback and test results for a new filter design, with suggestions for improvements. | 21th Sep 1928 | Box 44 \ 1 Scan233 | |
| Letter from Benton & Stone Ltd. discussing feedback on a filter test and an aluminium sump. | 22th Sep 1928 | Box 44 \ 1 Scan234 | |
| Improvements to the autovac tank and Zenith petrol filter based on observations of a Bentley chassis. | 4th Oct 1928 | Box 44 \ 1 Scan235 | |
| Letter to Benton & Stone Ltd. requesting larger diameter filter plates and a sample of a light aluminium bowl. | 5th Oct 1928 | Box 44 \ 1 Scan236 | |
| Standardising a lighter aluminium pressing for the Zenith petrol filter bowl to replace the current heavy metal version. | 6th Oct 1928 | Box 44 \ 1 Scan237 | |
| Letter from Benton & Stone Ltd. regarding delays and modifications to petrol filters. | 8th Oct 1928 | Box 44 \ 1 Scan238 | |
| Alternative materials for Zenith filter covers, proposing a new lighter material. | 10th Oct 1928 | Box 44 \ 1 Scan239 | |
| Letter to Messrs. Benton & Stone regarding a request for a modified filter due to unforeseen delays. | 16th Oct 1928 | Box 44 \ 1 Scan240 | |
| Letter from Benton & Stone Ltd. confirming that tooling for modified petrol filters is progressing well and a sample will be available shortly. | 18th Oct 1928 | Box 44 \ 1 Scan241 | |
| Testing of various fuel feed filters and their respective advantages and disadvantages. | 19th Oct 1928 | Box 44 \ 1 Scan242 | |
| Analysis of European and American Zenith Gravity Filters, noting their performance and disadvantages. | 19th Oct 1928 | Box 44 \ 1 Scan243 | |
| Testing and comparison of different fuel feed disc-filters. | 19th Oct 1928 | Box 44 \ 1 Scan244 | |
| Technical note on the performance and disadvantages of European and American Zenith Gravity Filters. | 19th Oct 1928 | Box 44 \ 1 Scan245 | |
| Letter to Messrs. Benton & Stone Ltd. regarding a petrol filter sample and requesting more for testing. | 27th Oct 1928 | Box 44 \ 1 Scan246 | |
| Request for two more modified Benton & Stone petrol filters for testing on experimental cars. | 27th Oct 1928 | Box 44 \ 1 Scan247 | |
| Letter from Benton & Stone Ltd. regarding the development and supply of experimental petrol filters. | 29th Oct 1928 | Box 44 \ 1 Scan248 | |
| Recurring issues with leaking or breaking glass on Zenith filters. | 29th Oct 1928 | Box 44 \ 1 Scan249 | |
| Letter to Messrs. Benton & Stone confirming stirrups will be sent. | 30th Oct 1928 | Box 44 \ 1 Scan250 | |
| The breakage of Zenith filters and replacing the glass covers with metal ones. | 30th Oct 1928 | Box 44 \ 1 Scan251 | |
| Breakage of Zenith filters and the urgent need for spare glass and a permanent solution. | 30th Oct 1928 | Box 44 \ 1 Scan252 | |
| Supply of spare glass for Zenith filters and a proposed new metal cover. | 31th Oct 1928 | Box 44 \ 1 Scan253 | |
| Sending a sample of the latest standardised type Enots Petrol Filter. | 28th Nov 1928 | Box 44 \ 1 Scan254 | |
| Providing feedback on the design of an Enots petrol filter sample. | 19th Nov 1928 | Box 44 \ 1 Scan255 | |
| Internal request to order two dozen cork washers for a petrol filter from Messrs. Benton & Stone. | 14th Nov 1928 | Box 44 \ 1 Scan256 | |
| | | | |
